Boca Bearings is a good supplier, just match ID, OD, and thickness, usually in mms.
To get the bearings out, remove the crank then heat the crankcase block in the oven at about 200 degrees, suggest not over 250. Take the heated block out and gently tap the case on a block of wood and the bearings should fall out. Rear bearing first, then the front is easily removed by pushing out with a dowel.
Do the opposite for installation, but use the crank as an alignment fixture. Heat the case, put the rear bearing on the crank, then install the crank in the case. A GENTLE push with a large dowel will help to insure the bearing is seated in the case. Put the front bearing on the crank snout and push into place with a wooden block with hole in the center. Use a press, or large vise, with wooden blocks to keep from brinnelling the bearing balls into the races. Tapping here is a no-no, too much chance of ball damage.
Hope Randy agrees with the above!