The Diamondback is built on Colt's smallest frame, the D-frame. It may use any currently made stocks marked for any D-frame, including the Police Positive Special, Detective Special, Cobra and Agent. (Note: the length of the butt on the D-frame was changed about thirty years ago, but stocks for the older guns are not generally encountered.)
The Python is built on the I-frame originally used for the Official Police. Stocks are interchangeable between these models. The original Trooper, made through about 1970, is also an I-frame and may use the above stocks, but be aware that the later Trooper Mk. III and Trooper Mk. V use different stocks.