The "wheels" are properly called "sheaves". You can frequently find replacement sheaves many places. Both blocks are made by Schaefer
and you may be able to find the exact replacement sheaves for them.
The hard part is that both the axle and the mounting hardware
are not intended to be disassembled. The rivets have to be drilled out to remove either the block from the mast or the sheave from the block. The mounting rivets look like aluminum
and will be much easier to drill than the axles. In that size the blocks are not expensive, it may just be simpler to drill out the rivets, purchase
new blocks, and then put it all back together.