I have these 4x8 wood panels in my mid-century house. I love them and they're in most rooms. The girl that grew up in the house stopped here yesterday and gave me a wonderful history of the house. Apparently, some panels are missing in certain rooms. I would like to restore them back to their original state. Can anybody tell me what these panels are, what type of wood, where they originally came from, and where I could maybe get them now? Thanks everyone! PS. The pencil is just for reference for the size of the wood grain. It's a pretty tight grain. 
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Like Leif, I was also going to suggest Luan, or Phillipine Mahogany, based on the detail photo. The wood grain looks a lot like the veneer commonly used on hollow core doors here in the US during the 60's and 70's, and still available today. It would have to be stained to be the color of your walls however. Often these doors are described as "Mahogany Veneer" but I do not think that is entirely accurate, as the wood is not the same as the mahogany one normally associates with fine furniture.
http://www.woodworkerssource.com/blog/wood-conversations/mahogany/
Yep, almost certainly luaun. Often sold as "Pillipine mahogany" back in the day as Leif says. Popular for hollow-core doors and underlayment grade plywood back when you could get good quality. In the US, plywood is typically standard 48 x 96 inches, though oversize sheets of certain grades are available special order or sometimes from specialty dealers.
I haven't seen a decent-looking sheet in close to 20 years. You might try plywood specialists. Places that carry cabinet, furniture, and marine grade plywoods.
Drat! I hate when that happens!
Oh, well. I guess this makes it unanimous. Great minds, eh?
Yeah, new Luaun barely looks like the old stuff. I have a bunch of old Luaun doors in the house and needed a new one, and the replacement is so different. It may just be that the new veneer is about as thick as tissue paper, while the old veneer was notably thick for veneer. Maybe 1/16 inch.
You might actually look for some old interior doors on Craigslist. They might be the best match. You would just have to figure out a reasonable way of removing the front and rear faces.
A door won't provide a 4x8 foot panel, though...unless you want to redo the whole wall in door-sized panels.
Cabinet-grade plywood is available with various species of wood as the veneer but you will have to go to a specialty shop to get it, or order online. Google "exotic woods plywood" for online sources. You can probably find something with a very similar grain that can be stained to match. There are a lot of different wood species available.
Sorry I'm late getting back to this. I had friends in town for the last week and did not get to internet much. First, I want to thank everybody for your replies, input, and information. I added some new pictures that were requested for the "swirly" parts of the grain. Aside from that, here is a little more detail about the house and the walls: The house was built in 1958 in NC. The panels are actually 4'x7' (or very close to that) and not 4x8, unless they cut every panel in the house down to that size for some reason. There are about 10 full sized panels throughout. Also it's hard to say, but I really think the panels are 1/8" thick. They seem like they could be reversible as well. I've had a hard time trying to find anything close enough to it online.
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