You can still buy new 6 lug split rims (although technically these aren't true split rims; even though we all refer to them as such) from Toyota. IIRC I paid about $125 each for the last two I bought. Of course that was in Riyadh so probably a bit more here.
Any truck stop that handles tires (or any tire shop that specializes in 18 wheelers) shouldn't have any issue mounting tires on those. I have no idea where you would get one of those rims "straightened" any more than I would know where to take a regular rim to be straightened. If it's just the retaining rings then those can also still be purchased new but the only place I have found them is in Japan.
The rims don't seem to be available from US dealers (maybe special order?) but they appear to be available in Canada even cheaper than I paid in Riyadh:
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