The part has been discontinued so you can no longer purchase it through a Subaru dealer. Even the pump is discontinued so that's not an option either. You can find a parts car or order a remanufactured unit from an aftermarket supplier. You might also try calling SVXFiles, he has a good selection of parts laying around. Best to call, he's hard to get ahold of electronically.
http://svxfiles.com/
Good luck!!!
Part number for the switch as a reference - 34428PA000
You might also try contacting the companies that rebuild them like AC Delco, Lares, A1 Cardone, they don't list the switch separately on Rock Auto!