i went through this mess as well a couple months ago.
just know that if you buy one from a private seller, they won't be able to ship it..i was told from numerous people that used gas tanks can't be shipped.
but if you buy it new (like i had to... $415 at the time), they CAN ship it.
also know that when you replace the gas tank, you might as well replace the filler hose (the biggest one attached to the top of the tank.. it's the hose you pump the gas into)
because when you attach it to a new tank, the decade-old rubber hose may leak (mine did).. this is a japan-only part, so order it as soon as you can to allow it the appropriate time to get to you.)
and you have to drop your subframe to replace the tank, so put aside a full day for the procedure (in case anything goes wrong)