I don't know about a Rikenon, but a quick search for "50mm f1.2" on Ebay showed up several 50/1.2 lenses for $150-500, depending on brand and age.
That's because the lens in the picture is a Rikenon 55mm f/1.2. They have a larger front element. Do an Ebay search for "55mm f1.2" .. I didn't see any Ricoh models, but a lot of Nikon and others.
There's much more keystoning than barrel distortion in that photo. It's made with the Voigtländer 12mm, so is 23mm EFL. Whenever you tilt a lens with that wide a field of view, you get keystoning no matter how good the rectilinear correction is.
Yes, I shoot with an EF 16-35 f/2.8 L USM, and a TS-E, so I understand the perspective issues, but that gives straight lines, and I saw two distinct curves on that sample: the building just off centre, and the inner building on the right. But on closer inspection, the centre building is slightly stepped and the curve effect comes from anti-aliasing. The building on the right is still a mystery, given the shape of the curve.
Numerous 55mm f 1.4 Rikenons have sold for $42 - $70 - seems like a pretty good deal.
