Are you talking STI Japan wheels or STI USA wheels?
You can get the US version from your local Sub. dealer or online:
https://www.subarugenuineparts.com/p...feff8d1e4f6c06
The Japan version can be ordered from Japanparts.com :
https://www.japanparts.com/parts/detail/41618
The US set will cost you around $1400-1500.
The Japan set will set you back around $2,000.
The US set is 17x7, whereas the Japanese set is 18x7.5.
Alternatively you can keep an eye on the marketplace as a few Series.Blue owners unload their US sets there at a discount.