oohh.. Yeah you're right.
The chances of finding those betas is slim, if it exists.
Still, I think people should know that unlike Arwing Landing (Biggest Starfox site) Says, there are WAY more then 3 protos, which they said were an unplayable pre-recorded demo, the alpha, and release cantidate.
The TRUE way goes like this:

Video demo
Tech demo (Leaked, unemulated)
Alpha (Leaked)
Late Alpha (Unleaked, but SNESorama owner has (Incomplete) source code)
Mystery proto 1 (SNESorama owner has source bits)
Mystery proto 2 (SNESorama owner has source bits)
Build 1125
WCES beta
Release cantidate( Leaked from source code)
--Final version WOULD have gone here--