There are many many opal dealers. My vote goes to Tim Thomas of
Tibara Opals in Clovis California. (http://www.opal-tibara.com)
He's been a dealer for many many years, is well known in opal
circles, has an excellent return-if-unsatisfied policy, and is just
an all round likeable gentleman with a delightfully wry and friendly
sense of humor. Usual caveat: no commercial connection, just
occasional customer and friend.