Any of the vendors on here, Google, search on here.
There isn't much you can do with a 2.5i unless you go turbo or supercharger. Or suspension upgrades.
Do you have E85 fuel in your area? If so, grab a used set of GT injectors from the classifieds and get a tune for e85. That's your best bet Imo.
08 Legacy 2.5i SC
98 Impreza OBS