Have you tried these guys?

Beeman Precision Airguns
5454 Argosy Drive
Huntington Beach, California 92649
714/890-4800 or 800/227-2744 (Orders Only)
FAX 714/890-4808
http://www.beeman.com/

I have a Beeman R7 which I outfitted with a cheap 4x15 scope off
a 22 rifle. No problems with the scope for a few thousand shots
and counting.
It's sighted for about 30 feet and I can consistently hit aspirins
at that range. Dozens of gophers in my front yard have given their
eyes to my pellets when they stuck their damn heads up out of
the holes.
Art

"Gunner" wrote

Any ideas about a rear sight?
Gunner