I've located several Albrecht bound volumes for people but have only heard one time about the blank covers being available and that was from Nick Koopman. That was over two years ago and I haven't talked with him recently let alone about the covers. His web site was very helpful but over the past many months it isn't working for me and I don't know what he has on hand. Hope this was a little help.

Have you tried eBay France ? They have quite a lot of National Geographic publications on sale