Jalapeno has some available now that are supposed to be pretty good:https://authenticautomotive.net/new-products/
TRANSMISSION MOUNTS FOR 1955-57 CHEVY CARS
These new transmission mounts are much more durable than any other aftermarket reproduction mounts for 1955-57 Chevys on the market. The rubber is tightly vulcanized onto the metal core and will not separate like the others. Thorough testing over many months have proven these mounts are far superior than other aftermarket mounts. These fit original transmissions only.
CM-045 Powerglide Transmission Mounts $39.95 / pr