SylvanLMP
You in luck living in NY State.
All you need to do is contact a local Master plumber.
Have this LMP do what I did in Wappangers falls and Beacon and that is install a Lead shower pan using 4 Pound per square foot (PSF) sheet lead and 6″ walls on each side.
By having a highly skilled LMP you can have almost any sized shower pan custom made to fit this space.
Good luck.
