What size speakers are in a 2007 Scion tC I only have one that works in the inside

 

6.5in and you will prob need a mounting plate for each. The rears are bolted in and I believe the fronts are riveted in (have not had my door panels off but have see at junkyard). If you don't want to cut the stock connectors you can also get adapters.

If you are just looking for a stock replacement I got some Kenwood 2-ways last year on sale at Best Buy for $20ea pair (KFC-1666R)