Try out this site:
Car Speakers | Component & Replacement Auto Speakers
I just recently did a change-out of all 8 speakers with Infinity Kappas.
3-1/2" in Dash
6-3/4" in Rear Hatch, Rear Doors, & Front Doors
You can use the factory speakers as mounts for the new ones. If you want, I'll post some pics. Don't worry about adapter rings.
Also get 6 of the Toyota Wiring Adapters...you can re-use the connector from the old dash speakers. There is a thread somewhere on that by "darkdane".
Don't forget to get the Bass Blockers for the Dash Speakers. I used these:
PAC BB-1PR (BB1PR) Pair of 6x9 Bass Blockers / Passive Crossover
I did not touch the Head Unit at all, and don't foresee that I'll need to. The system sounds way better than the Factory Install. I am getting a much better dynamic range from the lows to the highs, instead of the mushy mid-tones from those wimpy factory speaks.
While you have those door panels off, might as well remove the lights so you can upgrade to LED. And get some Sound Deadener Material...I ended up using 6 sheets of 18" x 32".
Good luck with your mod...