These optional electric motors for the 55-57 come up on eBay quite a bit. Sometimes they come up locally, too. You shouldn't have much trouble finding one.
I have one on my 55 2nd. They are noisy.
Another thing you can do is add a vacumn canister in your line between manifold and wiper motor. This helps to keep your wipers moving when you slow down or idle. These canisters are usually plastic black balls and about the size of a tennis ball. They are found in later model cars. Easily found at the salvage yards.
Best of luck
