Does anyone have a source for 12" center plates. 14" and 16" are common nowadays but I can't find a 12" except for maybe Ronsco in Canada. I only need one.

Railroads where I have worked have made their own center plates. But it is a big job. On a typical body center plate the donut is 1 1/4” thick and the backing plate is 3/4” thick. I usually increased the backing plate to 1” thick. Not enough of a change to make any difference. The backing plate was made to match the old plate except the center was bored with a 4” diameter hole. The donut would be made from 2 1/4” inch thick material. Depending on how much service the car is to get, material on a few cars was pre hardened 4140. The bottom side of the donut would be turned to appropriate diameter, 9 3/4 ?, and an appropriate radius on the bottom to match the radius on the truck bolster. On the top of the plate turn 1” thickness to a 4” diameter to fit in the 4” hole in the top plate. Drill appropriate hole for the center pin. On the OD of the 4” diameter of the bottom plate and the 4” ID of the top plate put a 60 degree bevel, about 3/4” deep, for welding. The reason for this design is I have seen to many welded center plates where the weld around the OD of the donut wore away leaving the donut moving in the truck center plate with only the center pin keeping the car on the truck. We welded with 5/32 flux core wire and a work rotator. The v groove weld on the top was welded full and the quarter round fillet welded around the donut on the bottom was also welded. With a big wire feeder and a rotator this takes a while, but the welder just stands there watching and making adjustment to rotator and wire speeds. The AAR recommended a slight bevel on the sides of the center plate, but I was not a big believer in this and it was not done of plates we made. On large plates I think we increased the 4” diameter keeping the weld close to the center of the radius.