I have searched far and wide the whole universe of computer shows, catalogs and the internet and discovered that only Fostex carries those exact same caddies for their D-90's, D-80's, D-etc.
Which makes them - fact: expensive to obtain.
Solution: I opened the case, took the railings from the caddy that Fostex provided and replaced them with the railing that came with the caddy I bought for $9 at a computer show. At that price, I was able to buy to extra caddies. Now, I have two extra "reels". The drawback of HDR sytems now with me does not apply.
Good luck, but hey, if you are not that adept at opening electronic equipment, get someone who is more technically inclined to do so for you.
Tony A.