Anyone know where I can get one?
Anyone know if one even exists?

 

I dont think such an adapter exists at the moment. I think your best bet would be to contact these guys and see if they can make one for you:

http://www.transmissionadapters.com/index.htm

 

Thanks fo rthe information. Never knew that company existed. I'll send them an Email and see what they can do. I'd be suprised if they could help.
I might just scrap the whole idea and get a Chevy transmission and a divorced transfercase

 

That won't do any good; Caddy's don't bolt to Chevy trans either. You need a Buick/Pontiac/Oldsmobile (called B-O-P) boltpattern trans or an adapter plate from TCI or other trans builder.