The Mossberg 590 / 590A1 riot gun is designed to take a modern bayonet (M7 or M9). An M1917 bayonet won't fit.
M1917 bayonets were made as recently as the Vietnam war, for use with Winchester M97 riot guns. These late-model M1917 bayonets have checkered plastic grips and Parkerized blades. They're rare and expensive.
The cheapest M1917 bayonets (other than the reproductions) are probably the ones with British markings, made for the Pattern 14 rifles. These are identical to the ones with American markings. There are even some with the British markings struck out, and overstamped with American markings.
You can expect to pay $225 for a good, original M1917 bayonet.