For parts try WEST MARINE or BOATUS etc. You'll probably get similar
prices at your local boat repair stores AND get useful info just
talking to folks. If the prop won't turn, drain the drive and see if
there is A) water in the oil
OR B) no oil.
A common cause of outdrive failure is fishing line wrapping around the
propshaft and gradually destroying the shaft seal, allowing the oil to
go out and the water to go in.. Pull the prop (no, you don't need a
"prop puller" on an I/O) and see what you have.
Don't ever run the motor for even a "minute or two" without water being
supplied to the outdrive water pump intake. If you do it'll ruin the
water pump and then the exhaust flappers will burn away and and and...
Good luck!
Mike