Hi Susanne, this sounds like what I just read in someone's new book about a plant he's looking for.
I definitely hope he finds it, his intentions are certainly noble.
If Golden Gate Orchids or any of the others previously mentioned don't work out, maybe try contacting Dwayne Lowder of Dowery Orchids; even if he doesn't have it on hand, I think he has good connections with at least one nursery/exporter in Malaysia or thereabouts and might be able to find this species.
Jan Smyth (autumnimports on ebay) also seems to have one of the more extensive bulbo collections around, including a lot of very unusual and rare species, and likewise might be able to help locate macrobulbum even if not directly sell it. Hope this helps!
--Nat