Tradewindsfruits.com has seeds. I believe they are fairly fresh since I didn't see them in stock until a few weeks ago and they might harvest as people purchase.
I haven't grown citrus seeds from tradewinds before, but despite other experiences I've seen on here, I've had almost 100% germination from seeds I've purchased, and I've gotten a huge amount of recalcitrant seeds as well as longer lasting tropical seeds from them.
Anytime they haven't germinated/got messed up it was from personal error like leaving them outside and them getting too much rain or sun. So I would recommend them before ordering from Japan, and you can get 100 seeds for $12.
I may have missed somewhere saying they don't, but it also looks like they ship to you.