Last year, after 30 years of exhibiting at the American Gem Trade Association GemFair in Tucson, Ariz., Omi Gems celebrated its best-ever show performance. So imagine the surprise and delight that greeted the Los ­Angeles–based jewelry manufacturer on day two of this year’s Feb. 5–10 gathering when a single transaction easily beat the 2012 total.“This morning, we had a sale that was more than all of last year,” said vice president Niveet Nagpal. He declined to specify the sale total or divulge any details about the buyer except to say that he was a retailer from the Midwest. Nagpal added that the sapphire necklace that accounted for the bulk of the record-breaking sale featured certified royal blue sapphires from Sri Lanka.“There’s a real appreciation for high-end quality jewelry that’s locally produced in L.A.,” Nagpal said.For students of the trade searching for clue