Morning all, my 2012 SRAM Force Carbon right crank arm has died, the carbon has deteriorated around the pedal retaining nut which is now wobbling and about to shear off. I'm loath to replace the whole crankset when only the arm needs replacing but I'll be jiggered if I can find anywhere to buy a replacement. Does anyone know of any such purveyor?

If not, a second question begs, I can find a 53x39 crankest much cheap, but it'd be replacing a 50x34 compact - I'd actually rather have the larger rings but wonder if I'd have to do much to the front derailleur or if the addition of 3 teeth makes a negligible difference to the diameter (I could do the maths but would appreciate any advice from anyone who's already made a similar replacement).

Many thanks in anticipation.