Didn't find any good website with a (google) map of wallyball locations across the world. Found some good clubs in Detroit. Found (and now talking a lot to) another club on other end of the globe - Australia. Quick searches shown nothing in Europe (and no interest of any racquetball-court owners to add the holes for wallyball nets when we traveled there to promote wally).
So I'll just post 1 known U.S. location here and feel free to add Yours in:
- Pennsylvania, Easton (on border with New Jersey):
Northwood Racquet & Fitness Club (northwoodrfc.com) has about 4 regular groups having 6-12 players each on average, plus some occasional groups here'n'there.