I guess I'm a little confused.
When you did your SRW 'conversion' you started with brand new steel wheels correct?
Were they bent (un-straight) when you received them? Or have you bent them in your travels?
Have you ran the rim only on the machine to confirm that it is the rim and not the tire causing the problem?
I would do that and put a dial indicator on it so you will have the specs of how far it is out when you contact people.
I think your best bet would be companies that restore classic car steel rims as in most cases it is cheaper to replace a modern steel wheel, then repair it. The only problem is I'm sure the wheels they deal with normally are 13-15 inch diameter and 4.5 to 6.5 inches wide, so your giant (to them) wheel(s) might not fit on their machine.
Of course if it came bent, the seller should warranty it.
When I bought my super singles I had hear the tires (Falken WildPeaks) could be hard to balance in the very large sizes, so I confirmed will the seller they would taken back any that where too far out of balance.
Mine results were: 3 needed less then 1 oz, 2 needed about 2-3 ozs and 1 needed 7 ozs, and they run (when warmed up) like a ninja walking over ricepaper.
I've had an interesting waterfall of failures from one event - the PO had a set of new tires installed soon after he bought them (enroute home with the vehicle) and the lug nuts were MASSIVELY over-torqued.
When I brought the Fuso home after purchase, it was a huge effort to remove the frozen-on lugs, especially on the passenger rear hub. They all looked okay (threads were fine) but in retrospect I should have stopped right there and replaced the studs, but they seemed fine and it is a big job to undertake unless truly necessary so I didn't.
In September we did a ~6000 mile road trip in the Fuso. On the way home I noticed that one of the studs had broken off that right rear hub. With no parts and no way to fix it, we continued home.
At home, it took a huge effort to pull that wheel off -
I'm pretty sure that the loose/failing lugs allowed the center of the rim to bend over time.
So far, the total carnage from one road service technician 'snugging' on the bolts with a big truck impact wrench-
PARTS
1 - rear hub assembly with inner/outer bearings and seals
7 - studs
1 - SRW rim
LABOR
30+ hours - the bulk of it to get the rear hub off the truck and separated from the brake drum.
SUBLET
balancing/checking 5 tires (rebalanced the spare for completeness)
I'm now running what-was-the-spare in place of the bent wheel and have relegated the bent rim to spare duty until I get a replacement.
On the plus side, I've had a chance to go into both the front and rear hubs and now know how to do it (I think)