Look in the children's section of watches.
Some are darn-tootin' small (I know my 7 yr old has some small watches).
Cut off the bands but keep all the mechanisms in place.
You might want to pop off the plastic / glass.
Then FIT (not glue) it into the clocktower / building face from the backside of the wall. Leave the roof detachable to that you can replace the battery.
I'd advise against the Mickey Mouse model, but maybe you're modeling ToonTown
Now, if you figure out one for N scale, let me know!
Cheers!
--Mark
