I was looking around on the Wookieepedia, and found this http://starwars.wikia.com/wiki/AT-AP_Walker

It says many fell into the hands of the Alliance, so I was wondering if there were stats for it anywhere.

I checked here already; http://swrpg.viluppo.net/transportation/vehicles/category/38/ but I didn't see it, so is it out of date or are there no AT-AP stats?

Nope, none.

A good stand-in might be to take the AT-ST, replace the weapons with a light blaster cannon turret and a medium laser forward with a note that it can't fire and move in the same round...