Correct me if I am wrong, but aren’t the tires just a cheap substitute for bumper plates? Usually the tires have a larger diameter, as well.
I had a homemade super-yoke that I made of flanged pipes and tires. It worked quite well. I would put the tires on the bottom to cushion the impact and stacked the weights on top of the tires.
Not sure where to buy them, but they should be incredibly easy and cheap to make yourself. Go to a salvage yard or used tire store and get a set of crappy tires with the wheels still attached. Go to home depot find 2 large washers that fit the diameter of your barbell sleeve. Drill the washers into the wheel on each side and you’re done.