Modeline lamps  

Does the tall floor lamp have any Modeline marks on it? I have the same design except in table height, but is unmarked.
For that cylinder design, you should be able to make your own replacement shade fairly easily with the watercolor paper of your choice. Test a few weights to see which translucency works best for you.
For the conical shade, a DIY effort is still possible, but more complicated due to exposed top and getting the template shape correct beforehand.

Thank you for your help, cdsilva. Yes, both lamps have the same label on the top socket. I can't make out the numbers, but they say Underwriter Laboratories, portable lamp, Modeline Lamp Co. My husband doesn't want to replace the shades, as he thinks that will decrease the value. He is all about leaving things original. Any thoughts on that? I don't know how you could possibly get the original ones looking much better.

The lamps in the condition you have will not be as valuable compared to examples in pristine condition that's out there (unless the 2 you have are the only known examples in existence or they used to belong to someone very famous). People who buys these things for investment purposes always acquire examples in the best and as close to original pristine condition as possible.
The shades can be remade or replicated by professionals or by yourself if you have the skills and tools to do it to make the lamps presentable if the current condition bothers you. If they are fine the way they are, use them and leave these lamps alone as they are. If you decide to make new shades, save the original shades in their current condition, stored properly like a museum conservator would so you can reverse it back if you change your mind later. Make a template from these shades without adding damage before you store them.
Find enough fabric with the same weave and color as close to the original and if I am not mistaken, linen(?) is probably the closest and if you prefer, you can find unused vintage materials, it will take some effort, time and money but this is possible.
The plastic part is Mylar (not Acetate) or similar heat resistant in matte translucent white that comes in different thicknesses, in sheet sizes or rolls if you can find it. CAD made this material obsolete when it was used to draw on with ink pens by draftsmen but there are also other applications so it is also possible to find this new or unused vintage just match the same thickness as what you have.
Make the new replacement shades as close to the original as possible and always disclose that the shades are replacement if you decide to sell them later (include the originals if you must).

If these were some early Poulsen Henningsen lamps, or something similar, I'd agree that the shades should be replaced only as a last resort. However, Modeline made a significant amount of these designs, which were inspired by early, more limited, Danish designs. If you are looking to sell, I believe that good condition shades (new or old) will bring a higher price than original bad condition shades, as most buyers will be looking to use these lamps and not purchase as an investment,
And as minimoma already said, if you plan to use them and don't mind the condition of the shades, then don't do anything.

Another conservation technique that you can also try (again if you trust that you can do this yourself without adding more damage to the shades) and assuming that the plastic part of the shade is not brittle or close to disintegrating when handled is the LOWEST heat setting of a hair dryer (remember, your goal is not to melt but apply just enough heat to get rid of the dents/wrinkles after it cools down), it will not be invisible or make it look like brand new but flatter and less wavy/wrinkled. There area also fabric tapes/adhesives that you can use to secure the edges of the shade to the wire frame. If you can imagine or picture the repairs in your head, you can probably do these yourself but if not, hire a professional to do the work.
Repairs on the shades can only be done properly if removed (does it unscrew?) from the wood base. Vacuuming the shades to remove all the dust accumulation before any work is done is highly recommended.

Thank you both for all of your help! I think we are leaning towards working with the existing shades. I was told they are fiberglass; would that be correct? There is some water staining and yellowing. Is there any way to clean them safely? Are you saying that to use the hairdryer on them, they would need to be removed from the frame, first? They do have screws, but I'd hate to remove them, & then not be able to get them back on correctly. And the fabric tape is a great idea for the area where the shade is torn from the frame! Thank you!

midcenturygrl,
Hire a professional and don't attempt any conservation work on your own if you have not done any of these sort of work before. Most here at DA have years, decades of experience doing these kind of work.
Try reading up on some books on basic general maintenance/caring for your collection and in no time you will build up enough background to tackle these kind of work on your own.
Try public libraries if you are near one like this small book called Collectors Compass (1950s and 1960s) from 2000, the title sounds cheesy but it is packed with good information and it is one of the first books that promoted designaddict.

Thank you, Minimoma. That is very good advice! I live in an area where it would be difficult to find someone who would know how to do this, so I will probably just leave them as they are for now. I will definitely check out this book, & keep learning!