Apple is now selling the wheels and feet separately from the 2019 Mac Pro via individual kits, but like the Mac Pro itself, both kits are pretty expensive (via 9to5Mac).
If you configured your Mac Pro with the standard feet and want to give it some mobility, the $699 Mac Pro Wheels Kit gives you four stainless steel wheels you can install. But you should be aware that the Mac Pro’s wheels are cheaper when you buy them as part of a Mac Pro configuration — they cost $400 when you buy them that way.
The $299 Mac Pro Feet Kit gives you four stainless steel feet you can install on your Mac Pro. If you configured a Mac Pro with wheels when you bought it, you can install the feet to make sure your Mac Pro won’t roll around.
Apple says both kits come with a quarter-inch to 4mm hex, but that “additional tools are necessary” for installation. Both kits are available to order now.