We have purchased this kind of item in the past and believe there is no other way to do so that is as simple and inexpensive as through Appliance Factory Parts.
This item is a special order from the manufacturer. Your order will typically ship in 5 to 20 business days.
Swivel caster (locking) - for: mmb10, rm
Swivel caster (locking) - for: mmb10, rmmb12 & rmmb14
Buy this part and as many parts as you like and pay only $9.99 shipping, within the Contiguous United States.