All of the 12 inch rims supposedly have the same 5 bolt pattern for weights, so you don't necessarily have to get them from your dealer. I have turfs on my BX2230 and have 10 gallons of washer fluid in each one plus a gallon of water (just cuz they kept on taking more). That puts them at about 90 lbs. Beet juice will be heavier still, but perhaps the R1 or R4's don't take as much, or My442's are not filled to the 70% mark.
Some other member had made his own concrete weights a few years ago. Said they were about 200 each.