i just use normal insurance, you can use Japanese specialists, i think there are a few on the site, think sky and Adrian flux could point you in the right direction?
Unfortunately insurance is one of those things that it can be right for some and horrible for others, your best bet is to try the site sponsors, some comparison sites and who ever else you can think of.
One word of advice though, Direct Line wouldn't allow any modifications on my car when I had a policy with them. If you're intending to mod, they would be best left alone! I've heard Admiral are alright, I'm with Sky and they seem fine too!