I’m not sure if the 1956 shift handle you need is the same as 1958 10 HP, but if it is, I bought one earlier this year for my 1958 at a reasonable price from Ken Hall. You may want to check and see if he has more. Find him at: ken1401732@aol.com
The part number for my 1958 is 376308. If yours is different, Ken may have that too.
Dave