E-bay, just make sure you know vintage of your Python. There are 3 possible originals for your revolver.
FIRST TYPE: 1955 to early 1960's??
These were fully checkered, with Gold medallions on Pythons ONLY, Silver on other models.
SECOND TYPE: From early 1960's to mid-1970's??
These have the first "thumb rest" (actually a loading clearance) only on the left side, with the checkering wrapping partially around the Gold medallions.
RIGHT SIDE no "thumb rest" and curved checkering around the Medallion.
THIRD TYPE: Mid-1970's to the Python Elite of the mid-1990's.
The "thumb rest" is now on both sides, and the checkering ends in a straight line under the Gold Medallion.
Color began to lighten, and quality began to decline in the mid-1980's, with patch material sometimes used to repair defects in the wood or to correct poor fit.