Suitcase weights are pretty much universal. Larger tractors will have a taller bumper, so a deeper notch on the back of the weight, but weights made for a larger tractor are easy to adapt to a small bumper. Those Deere or Lowe's weights should be close enough to make them fit. Just measure everything before bringing them home.
I found a great price on four 43 lb weights for a larger tractor. I bolted in a chunk of 4x6 lumber to fill the gap below the bumper, and put a piece of metal plate on the 4x6 where the weights bear upward against it so the weights couldn't dig into the lumber. Everything fits snug like it is supposed to.
One comment if you decide to make your own weight: I think it is a mistake to put on a wide front bumper made from railroad rail or filled pipe. These tractors can turn very sharp and a long bumper will hit everything you are turning to avoid. Turn the front wheels sharply and note the outer radius swept by the front corners of the tractor - then design something that stays within that radius. Sticking weight way out front is harmless, in fact it gives more effective ballast per lb of actual weight, and is way preferable to making a wide weight.