Here are a few possibilities:
Thumbstick from arcadeshop.de
Grayhill battop from Allied Electronics. Other suppliers like Mouser carry it too, IIRC. This is what Bender used in his micro DK and Le Chuck is using in his micro Gauntlet.
Grayhill joystick from Allied

These Grayhill joysticks have a .850" square base. Darasheet
here.
BTW you don't need to solder on the Grayhill joystick pins. The joystick pins fit snugly into .100" header sockets like
this or
this. The spacing is wrong to fit more than one pin to a connector, but 5 individual connections works great. These box-style socket pins can be easily removed from the connector body.

CAUTION: The joystick pins aren't quite long enough to work properly with the commonly used ramp-style
KK100-type contacts like this.

Scott