My no no.s from DSS were around $1400, the 341's I got from cmsnl were around $1850 with trim. Around the time you got yours, DSS showed a few sets in stock. It was too late for a heads up to you, and I stupidly didn't order them when I saw them, the next day they were gone, and they have not had any since. I think they had been stuck in the suez canal!
My first set of Yamiya were from one of the ebay sellers, Mach IV motors if I recall correctly. I sniped them for $1200 and they stopped selling them after that.
I still think Yamiya's are made by M Tec Chukyo which is related to Mugen, which is/was owned by Mr. Honda's son. He made a prototype of a Vincent clone a couple decades ago, tried to get it into production. There is a welding shop in Japan that makes the 4-4 Yoshimura Daytona copy per order when they can.