Many high quality industrial valves are glass reinforced (sometimes called engineering valves too) - so trying any stockest of engineering valves should work. They usually have similar construction plastic pipe fittings as well.
If I might add to what John has said about the fittings, do ensure that whatever you buy, you CAN get the fittings / hose tails that you want.
I bought five Patay seacocks for my boat and ordered the hosetails also from Patay. In fairness to Patay the hosetails did fit and they did not leak but in my opinion they were not substantial enough and were only long enough to get one jubilee clip on...... They may be ok for canal boats but when that is all there is between me and the bottom of the deep blue sea I want something more substantial so then the hunt started for better fittings and they have proved very difficult to find.
I have found two different types of plastic hosetail and they both leak up the threads. I have tried PTFE tape and thread sealant without success. Sikaflex would probably do the trick but one day I may need to take them apart again.....
Perhaps I should stress that it is not the Patay seacock that leaks, the problem has been finding decent hosetails. In the end I have had to scrap the Patay seacocks and have ordered the Marelon cocks from Aquafax simply because they also supply a substantial compatible plastic hosetail.
'Hope this helps.
Paul.
<hr width=100% size=1>I used to have an open mind but my brains kept falling out.....