Every once in a while when the planets align, a fiberglass one does come up. I think I've heard of two, maybe three in the past fifteen years.
They're rare, and a good looking one (as opposed to one that looks like a dunce cap laying on it's side) are even more rare.
I found one on eBay or somewhere similar and bought it sight unseen (aside from pictures). Cory Drake graciously drive a couple of hours to pick it up, then built a nice crate and shipped it to me from the east coast. It cost slightly less than air-freighting chunks of Skylab back to my home in Buttscratch, Nowhere would have.
I'm never giving it up, so please don't ask. I looked for the better part of 5 years before locating this one.
I'll use it on Project X.