Lori, I’m sure you could find a charm to solder on, though I can’t
recommend where to find one. You could also make one with PMC, etch
the design into the silver using ferric nitrate, cut the design from
thin gauge silver sheet and chase the details, or you could probably
make one from silver wire and doing a little forging (hammering) to
flatten the wire. I’d either make one from wire or etch it.
What you are looking for is called the Staff of Aesculapius; it is a
single snake twined around a staff. This has evidently been confused
with the Caduceus, two snakes twined around a winged staff; the
confusion dates back to the times of Henry VII.
You can follow this link to find out moRe:
Searching with Google will probably result in many suitable pictures
of the symbol.
Christine in sunny and springy Littleton, Massachusetts US