Cadovius  

the slanted bookshelf could very well be a part of the cado wall unit. I have a poor picture of a similar one here. as for value  

It's got the wrong attachment hardware for either Cado system. 

Leif,
your knowledge of wood sets the bar on this forum, If I had a few questions on american colonial, l could you help?

Thanks. Further research found this site which shows it as Cado and the Royal system. Thoughts?
http://www.vintage-design-point.be/portfolio/hanging-desk-by-p-cadovius-...

Neither of your pieces are cado units. I don't think they used particleboard back when

My thought is that site misidentifies it as Cado.  But you now know what the system looks like. Go looking for more of those strangely shaped metal shelf brackets and perhaps you will find a marked specimen.
 
The black wall posts could also be characteristic. 
I would speculate that it might not be Scandinavian. Something else European. But that is just speculation. 

Or to quote auntie Mark, "I could be wrong"

I probably am wrong. It is too late tonight. 

I can look at this old high school book on woodworking if yours are the Cado units.  It is interesting that the current reissued pieces are so high end and so expensive when this book I have have exploded drawings/diagrams on how to replicate the pieces with permission from the designer and original manufacturer.  The book offers it as an affordable alternative well made shelf system for someone who cannot afford Nelson's CSS units for Herman Miller and other high end systems.
Particle board or press board was used a lot in Danish furniture (even for the older ones), it was used where a solid plank (which is prone to warping) is not needed and instead veneered on both sides.  The makers used solid wood where strength is needed like the edges, the legs and the rails to withstand breaking and denting.  The Danes were also very aware that the woods they were fond of using (teak,rosewood and others ) were not harvested in their own backyard. 

A few thoughts:
1) The mounting hardware on your pieces might work with the Cado Royal system; they would use pegs just like the cabinets do.
2) I believe all Cado stuff was particleboard with veneer.  I have older Royal components from four distinct sources and all are particleboard with veneer.
3) I've stared at a fair amount of Cado Royal stuff, and have some low-res catalog images that someone posted here, and I don't recognize your pieces.  The Cado cabinets I've seen do not have sides that extend beyond the top, and the 45-degree book / magazine display shelf doesn't have solid sides.  That's just what I've seen, however, and certainly doesn't mean they're not Cado.

What about Kai Kristiansen?
https://www.1stdibs.com/furniture/storage-case-pieces/cabinets/danish-te...

Yes. Looks like Kai.
 
Anyone have ideas on where to get rails?

Good morning and merry Christmas greetings to you all from a dark and rainy Denmark.
You are all slightly off the mark with cadovius and fm system. There were a number of different wall systems made in denmark.
Cadovius designed and made the royal system which has distinctive brass / chromed or black metal shelf mounts that fix into the side of wall brackets.
The cado sysstem has wood shelf supports with angled dowl fixture that fit onto panels or uprights.
Feldballe møbel fabrik which made the FM-system by kai kristiansen. The shelf /cabinet has integrated mounts in the back which fit into aluminium extruded uprights or cheaper bent metal uprights.
randers møbelfabrik made the PS-system which has several different shelf mounts. 1, similar brass shelf supports to the royal BUT had a screw fixture through the bottom of the shelf into the upright.
2, wood supports which have a triangular metal fixing plate that bridges the join between the upright and the wood undershelf support.
Cabinets are hung on using hook and pin design BUT also a metal fixing plate which has 2 pins on one side and a single the other. the 2 pin fits into the upright and the cabinet hands on the 1 pin. this hides the fixture in the side of the cabinet and. These were again Fixed into the side of the wall mount.
THIS IS WHAT YOU HAVE AND DUE TO THE SIMILARITY TO ROYAL OFTEN GETS MISQUOTED AS SUCH.
I spoke to PREBEN SØRENSEN's daughter about her dads design which is why it is called PS-system
HG-70 which was designed by RUD THYGERSEN & SØRENSEN
This system has distinctive wall mounts where the shelves have wood supports that have a small pin and plate fixture. The domed head on the support fits into metal plates integrated into wooden uprights.
The cabinets have integrated hook fixtures.
The metal plate offers 8-10 options of fixing with a small gab before the next plate begins.
I hope that helps a but but can sort some images if that would help.
Ho ho ho and all that.

Simon -
Wonderful information as always. THANK YOU!
PS. I would love see photos if you can scrounge them up.