You'd have to look for a parts camera most likely and even if you find one the front group probable wouldn't be optimum for the rear group you have. I tried to mate two 121mm Super angulons once. I dropped my 121 and broke two elements in the rear group and found one that had a good rear group and trashed front cell. I wound up sending them to Schneider to get the front and rear cells shimmed to mate properly optically.
As good as Schneider quality control was in those days each set of cells had to be mated optically to work at peak performance.
If you can find one you might get lucky but it's probably cheaper to buy another new one.
By the way they are excellent cameras. I like the one I have much better than the Widelux I had.