If obtaining a swiss or phill BB is not possible, you could at least fix 1/2 your problem by putting a good cup from a french BB into the right side.
Might also be worth a try to re-finish the existing slightly pitted cups (on a lathe) or try packing the BB with a fine abbrasive polishing compond instead of grease and riding for a few hours to see if you can polish out some of the pitting, then dissasemble, clean and install new bearings. I would re-pack with loose bearings instead of using bearing retainers, try to fit in an additional bearing. It might also be worth a try to use a slightly different size bearing, see if you can make it work with different size bearings that roll on fresh surface of the cups instead of down in the pits.