I got mine here
http://www.tcracing.org/
they're very nice
word of caution:
they will fit a momo style wheel, but not a momo-style hub
you need a raid or nardi style hub
(unless they changed the design)
so double check!
a momo-style has a 70mm bolt circle, with the bolts starting at 12 o-clock (then 2,4,6 etc)
a raid/nardi/personal style has a 75mm bolt circle, starting at 1 o-clock (then 3,5,7 etc)
IIRC, you can mount both styles of wheel to the quick release, but only the raid/nardi style hub