Saw an ad in Mother Earth News...thought it could be REAL helpful for some members. I'll be ordering a few items soon, I hope. I haven't seen anything on our site here, so sharing as I find...
I have made my own by simply cutting a piece of PVC the same size as I am using. I take a 4 " piece and cut 1/4th of the diameter out with a band saw and then just press it over the PVC pipe to hold my tarp or whatever.
We use these on our greenhouse. They're great, but ours finally got too weak after 2 years. So we've just ordered in some more along with the metal clamps that go on top of them to make them even stronger. It should be interesting to see how long they last this time. :)