No, R4s are not avialable for the BX, but honestly the bar tires that are available are very effective for traction yet generally will not damage your turf unless it is really wet. I had turfs on my previous BX2200 but switched to the bar tires on my BX22 after only a few hours. NO comparison. I wouldn't want to go back to using turfs with the FEL, etc. after seeing how much better the bars perform, especially for plowing snow.
Keep in mind that the bar tires for the BX are not exactly like the R1 tires on the larger tractors...they are much wider and "float" really nicely, but with nice grip when you need it.