you can get the relay from radio shack of most auto parts stores. hell, i think even wal-mart/canadian tire xmight carry them, too. just a basic 5 pin auto relay will do the trick.
as far as getting it fixed, any shop (other than who you took it to) is gonna be in the same boat that we are in. the only shop that has a clue what they did was the one who did the work. Id say take it to them, have them show you their work, and then you can take it to another shop so at least they would know where to start.
Good luck!
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2009 Corolla S : Kenwood Kdc-x993, Polk MMC6500, Polk db651, Rockford Fosgate T110D2, Alpine Pdx.5
Magnaflow 2.25" Muffler, TWM Short Shifter and Base Bushings, Summit Engineering Shifter Cable Bushings, Tein S-Techs, V-Leds LED's, Enkei RPF-1 (18x8 +35), Inno IN-SU Roof Rack.