Two options come to mind given you can't find the proper bearing size.
If the crank is .001 under
(bearing .001 thicker then stock), you may be able to use a standard set of bearings and shim the cap bearing with paper. Newspaper is app .003 thick, while an electronic receipt is about .002. Cut the paper about 3/4 the length of the bearing half and place it under the cap bearing, being sure it doesn't get under the lock tang. Plasticgage the bearing to insure you have enough clearance. I know it sounds like THE most redneck thing ever, but I have seen it done a couple of times and it worked (Jeeze, I flinch even mentioning it here
The other (better) option is to replace the crank with a .010/.010 grind. This will standardize your mains and rods. this fix will, however, be a bit more entailed.
Remember to check the clearances on the new crank as well.