My name is Ian and I live in western Japan. As you know, lots of BJ250 Estrellas here, along with their Enduro-based sister, the 250TR.
I don't own a complete Estrella, but am currently modifying and improving a rare old '70s 2-stroke road-bike using all BJ250 Estrella running gear - forks, steering head, brakes (front / rear disc conversion), awing-arm, wheels etc.
All excellent quality parts and all sourced from Yahoo Auction Japan. There are pages and pages of Estrella parts (new and used) and all at very reasonable prices.
Although this may not appeal to the purists, these BJ250 Estrella parts were a natural choice in terms of '60s~'70s period look with '90s quality and are being used to restore an otherwise scrap bike .
Yes, you are correct, Yahoo Auction is in Japanese, however there are some sellers who will also post parts overseas.
If anyone is interested in knowing how to navigate Yahoo Auction Japan to see what kind of stuff is being sold and for price comparison etc. please let me know, I would be happy to help with screen shots how to navigate etc.
Google Translate will then translate well enough to give you any details you need.
I can't post any links at the moment, but can do so in future when allowed.
I bought a few new things from japan, but the biggest obstacle was the language, as few sites offered any Latin based language as an option for communication...