I did a quick search and found an electric scooter wheel. Not sure of the size.
https://www.amazon.com/Universal-119...1033&sr =1-14
Also found this 5" wheel.
https://www.amazon.com/Dynabrade-944...Y51 YPV82MEFZ
This wheel claims to have a 3.25" hub.
https://www.zoro.com/b-p-manufacturi...f-00505694526f
Links for electronic skateboard
http://www.enertionboards.com/pages/...cnc-alloy-rim/
https://www.google.com/search?q=pneu...-FQGV_VtTlM%3A
Their might also be used by electric wheel chairs or hoverboards.
Another idea is to search for "rubber stroller wheels"
Dave