For the most part radials are no longer being manufcctured. In fact, back in the late 70's a company dealt with the problem of running out of rebuildable cylinders for R-1340 engines by taking the much more plentiful R-2800 cylinders and cutting them down to fit an R-1340. Aside from availability, the R-2800 cylinders used more advanced technology that extended their service life when they were "de-rated" by using them in an R-1340. Aside from T-6's, the engines were popular for crop dusters.
Looking a a list of engines in current production in 1946, I found the Continental R-670 conspicuous by its absence. I assume that aside from the end of Stearman biplane production there were so many 670's left over from the war that the company saw no need to build any more. The W-670 version was used in Stuart tanks and other vehicles, and the parts from those, the cylinders at least, were used for decades for rebuilds. You could not use the pistons from the W-670 in aircraft, so a gentleman I knew ended up scrapping many of them; I wish I had bought them from him to sell as genuine WWII tank mementos. Mount them on a block of wood with a little plaque and I think they'd be big sellers.
The R-1820's that came out of the B-17's served to supply needs for many uses after the war. The modified T-28A's the French turned into the Fennec light attack aircraft used engines from scrapped B-17G's.
The Soviets and Chinese kept building small radials after their war for their trainer aircraft but I doubt they still are. There is an outfit in Australia that is taking Rotax cylinders and using them to build small radials in the 100 -150 HP range with 7 or 9 cylinders.