Does anyone make aftermarket Knobs for silvertip bows(for bolts mounted in the riser)

You talking about antler or the the standard knurled?  I would contact Beth at Schafer Silvertip directly, they have what you need.  Binghams also has knurled knobs I believe.  I'm not sure anyone else supplies the antler knobs that go on riser mounted bolts, most of the other available stuff is antler on a bolt for a standard Allen attachment.

Call Beth, she'll hook you up with a set!

As stated above call Beth and Dave.

Have dave make you a set of BIGHORN sheep knobs that are knurled along the edge,PRETTY darn COOL.