Unless you talk to D&D or the other guy in Washington (Baker), you'll probably have to search the eBay or craigslist ads. There aren't many 215s on this site.
I bought most of all mine in various states. Michigan, Missouri, Tennessee and Oklahoma (I like road trips)..... either in a car or by it's self for parts. They are out there, just have to look..... and look often.
Using various searches on eBay like "Buick 215", "Olds 215", "215 V8", "aluminum v8", Buick Special 215, Olds F85 215, 3.5L v8, even Rover V8..... you'll get lots of hits.
Here's one for parts or rebuild: http://www.ebay.com/itm/1961-1963-OLDSM ... h8&vxp=mtr
Here's one complete: http://www.ebay.com/itm/Olds-215-Engine ... 85&vxp=mtr
Whole car with running 215: http://www.ebay.com/itm/Oldsmobile-Othe ... 2086007534
Don't forget to click on "Completed Listings" in the sidebar on the left when you finish your searches above...... the completed listings show the recent auctions that have ended.... green price means the item sold..... red price, item is unsold. Can really find good deals this way.... obviously, the unsold items....
http://www.ebay.com/itm/MGB-V8-buick-19 ... Zk&vxp=mtr
http://www.ebay.com/itm/Buick-215-Alumi ... B3&vxp=mtr
http://www.ebay.com/itm/VINTAGE-OLDSMOB ... Sp&vxp=mtr
Then......
Use searhtempest http://www.searchtempest.com/ to search ALL the craigslist locations with those same searches as used on eBay above.
Also, you'll need a '61-'63 215-specific bellhousing, as they are NOT Chevy nor Buick,Olds,Pontiac bolt pattern. D&D also has them as well as some conversion bellhousings. http://www.aluminumv8.com/
These guys have lots of parts and Info..... but they're across the pond: http://www.v8engines.com/
Here's a nice link to some parts suppliers: http://www.team.net/TR8/Vendors/USRoverV8list.html
Like I said, they are out there.... but you do have to search a bit more than say a small block chevy or ford.