Haven't used the Advan so I can't comment on that. I went from V700s to V710s a long time back, but while it is possible to drive to/from events on these, it isn't really advisable (I did this a few times on V710s until a rainy day came along and have been changing wheels after I get there ever since). If you have other wheels, then you might consider a good lightweight jack and just changing after you get there (and then looking at the V710s or Hoosiers or similar).
Other route would be trying to find someone with the V710s in stock... the following came up on Google and they weren't listed as out of stock, but doesn't mean they actually have them:
KUMHO TIRES VICTORACER V700 - Starting from $164.00 Featuring Free Warranty and Free Freight - Tires from Performance Plus Tire
Mazda Performance Parts: Kumho Ecsta V710 225/50-15 mounted and balanced!
Might be worth checking race shops that deal with a lot of Spec Miatas too as I think that is the same size typically fitted if they run V710s.