"There are 3 "types" of clear vinyl window material commonly found on boats. "Roll goods" are just that. The vinyl comes on a roll and is purchased by the yard, generally in .020, .030 and .040 gauge thicknesses. It's soft (that is, flexible) and comparatively inexpensive. It tends to have some inherent distortion when looking through it, although the newer varieties are much more clear.
The next type is "pressed and polished" window material, sometimes called "optically clear". The manufacturer presses two pieces of clear vinyl together and polishes it, removing the distortion. It's purchased in sheets in .030 and .040 gauge thicknesses. It's stiffer than the roll goods but is still easy to roll up.
The next step up is "Strataglass
", where the manufacturer applies a film to both side of the pressed and polished glass making it resistant to scratching and deterioration from UV. It is sold by the sheet, generally in only .040 gauge thicknesses. It has the same stiffness as the pressed and polished. The manufactures of Strataglass tested it under accelerated UV conditions and found it still good after 12 years. It's been on the market since 1994, and under "real" UV conditions, it still looks great."
Here is the link I pulled the above information from, which also includes dimensions and pricing:
You could at least use it to narrow a search for a local vendor or to compare prices from competitors. My guess is the OEM stuff is the cheapest they can get. I would suggest considering what you want on there rather than what the manufacturer gave you to start. It's my opinion that if you're going to repair/replace something then make it better than it was, if at all possible. (If OEM was a plastic part and there is a suitable stainless replacement, I go with stainless).