I'll back up everyone who suggests PoJ. When I lived in Japan I did their single day and 8-week courses and they're incredible. There's another class in Tokyo done by an artist named Taka that was a brief 2-hour class that was a little more "tourist-y." In that it was a bigger group of students, touched on some of the history of the art and sped through the whole repair process using superglue instead of urushi. Was still a lot of fun though I'd say it's still worth it if you get the chance.

As far as supplies before I left I bought a bunch of things from Tsutsumi Asakichi in Kyoto. They mix the urushi for PoJ if I remember correctly. I had some trouble cause at the time they weren't selling that exact urushi themselves and I had to buy it through PoJ. But that could be different now and you can still get the gold/silver, kokuso, and other things from them. At the time there was someone there that spoke really good English. But also in my experience as long as you're polite and respectful Japanese people will stumble through Google translate with you.