Dually tire service/installation

I've found having an appropriate quantity of balancing beads put in the tires before mounting easily solves the balancing issue. No machines needed...

Find a mom n pop shop or used tire place if none of the chain stores will do it.
Or take them to a Walmart tire shop.

And it is no more difficult than doing tires on any vehicle. And those little tires and rims don’t even command a premium charge for mount and balance.

I've dealt directly with "professional" tire shops that supposedly handled a lot of duals for commercial trucks, but came away with shoddy workmanship anyway. In a couple of instances, I purchased the tires from them.
Many times, I've had to take it back, explain how duals are supposed to be mounted on the hub, and that's after getting them to run a second balance.

Tire "professionals", indeed. It's easy to throw labels about.

There's an index hole (or pin) that aligns with the index hole in the rims. Then, the valves are supposed to be 180 degrees apart.
In my last case, they buried one of the inner valves - it wasn't even visible.
Idiots.

To Discount Tire's credit, they bumped other work, pulled the motorhome in and re-did all 6 tires, paying particular attention to the balance, then properly mounted them on the hubs. I checked their work before departing the second time.
The problem was a floor "manager" that was not qualified on the balancer was trying to help the workers with the work load. He learned his lesson - he should have stayed in the office, and let the qualified help do the job.

You could get Centramatic balancers for the rear. I installed them on my duals with balanced tires and they made a lot of difference. The instructions suggest not balancing the tires prior. The cost would offset your savings by buying tires at Walmart.

Find a "truck" tire shop.

Most tire shops don't want to install tires that you bought cheaper online. If you want to buy the tires from Walmart why not have them shipped to the closest Walmart store and installed there? Otherwise, why not buy them from the local tire shop? That size is pretty common, you shouldn't have any trouble finding what you want.

cannot balance the inner tires. Is that a possiblity? in other words, is he pulling my leg? Thanks for your inputs in advance.

Find another shop. Balancing the tires is done prior to installation.

Pulling your leg....
Tires are balanced before bolting them on, after mounting on the rim. It doesn't matter if they are inner, outer or on the front.