Most building codes will not allow a bypass door on a shower smaller than 54".....the entry opening is too narrow.
I believe LASCO used to make one, but it's distribution was limited to those few backwoods places where codes do not prohibit.
The makers of premade doors are Lasco, MAAX, Keystone, Sterling...among others. Century as I know the company is a custom manufacturer, and they would make you one if you want.
Why not get a semi-custom pivot door+fixed panel arrangement.?