For the 7" stocker trout, a #1 or 1/0 hook would be the right size. If you aren't seeing the bigger size treble hook in stores its because a lot of stores don't stock hooks that size. Here is the full lineup of Owner trebles on TW
You won't need any split rings to rig a 7" stocker trout, but if you are looking for split rings to upgrade baits with, the Owner Stingers are simply the best split rings available right now. A size 6 is good for attachment to a thin wire loop. For a heavy wire loop, a #7 or #8 ring is better. I won't fish my baits without these split rings, they are bulletproof.