Monoprice is an excellent source for quality kit at a more-than-fair price. Link below is for a standard 3' power cord for a PC in 14 gauge (at $2.99). They have some 12 gauge cords, but only for the 20 amp connectors. I messaged them that those of us running a high power amp from a standard 15 amp receptacle would really appreciate
a 12awg power cord option. Maybe if enough ask for it, they'll add it to their line!
https://www.monoprice.com/product?p_id=5289
https://www.monoprice.com/product?p_id=5289