It is my understanding that the custom chips can only come from existing systems, or dealers that have stock of old chips. I have to do some more research as to which Agnus chip will work, but I believe that the square shaped one from the A500, A2000 and A3000 is the one needed, in 1mb or 2mb (fatter and fattest Agnus) versions. I think the rest of the parts needed are still available from what has been said in that other A1000 Phoenix thread.
I have no idea what the cost will be, but the last run was reasonable, so if we can get 50 to 100 people interested, and/or a couple of the few remaining dealers, we should be able to justify the production.
Software Hut, Amiga Kit, Vesalia?

I don't think this will be worthwhile with just 10 or 15 interested buyers.