My preferred solution seems to be out of stock at ServoCity:
Hitec HSR-1425CR. It seems to be in stock at
RobotShop, however. ServoCity will mod most of their analog servos into a continuous rotation version for you for a nominal fee, but I'm uncertain as to the legality of that. On the one hand, it's not you modifying it the servo. On the other hand, the resulting servo definitely isn't factory spec after that.
EDIT:There's also
this monstrosity. That's a legal HS-5485 servo modded for continuous rotation and slapped into a gear reduction setup. You can get more torque out of it that way, though it's even slower. I think I might question your sanity if you picked one of those things over a window motor or something similarly sized but rather more powerful.