Automotive Tire for rig

I just purchased my sidecar rig, a 2009 BMW K1300GT with a new Hannigan, and I'd like to put an automotive tire on the rear, and a rear motorcycle tire on the front, mounted backwards. What is the best source for an automotive tire that will fit my rim?

Thanks for any help you have. Glad to be back to Sidecarist. This is my second rig, the last was a few years back.