Yes I do, No I havent, didnt even give them a thought, think they will have? I dont want ANY metal parts in the valve so still not sure if I should try them, their level of product knowledge scare me sometimes.
I have found plastic ball valves a builders at their garden irrigation area. Also BuCo sells them. I think most hardware stores should sell them these days as they have replaced most steel valves anyway.
The only place I could find proper gate valves (as opposed to ball valves) was at ECA Marine - I've bought from them a couple of times. I'm mentioning their name as I'm not aware of any sponsors who stock these - if there are, my apologies.