You might try Eddies Tire Service in Lewistown, if that's your neck of the woods. Many lager tire service shops will do it fine if you just tell them it's for a trike or sidecar. All that's needed is a standard rim clamp machine. They often won't be able to balance it, but Eddies does ATV stuff too, so might be able to handle that too. If they can't balance it, just take it to a bike shop for that.
Do take the wheel off the bike though and walk the tire and wheel in. Also, you might try the indipendant HD shops in your area. Many small indi shops are happy to take your money and mount what ever tire you want w/o issues.
