I had a Velbon tripod that I bought in 2002. It recently gave up the ghost, and I replaced it with another cheap tripod, a Targus TGT-58TR. To my surprise and pleasure, the quick release plate for the Velbon that I used on my big binoculars (11x70mm) also fit the Targus tripod. However: I also noticed a few days ago that the Velbon quick release plate was loose--in fact, the metal thumb screw had punched a hole through the cheap plastic of the plate.
I went to Idaho Camera--and they explained that every manufacturer's plate is proprietary, and they did not carry the Targus brand. I went back to Wal-Mart--but they do not sell the quick release plates for the Targus. I went to the Targus website--and they seem not to sell quick release plates for their tripods.
I went to B&H Camera, who sends me a camera porn catalog every few weeks because I bought something from them, long ago, but I could not find anything that explicitly said that the Velbon quick release plate that looks much like the broken plate fits the Targus, and they are closed for a three day weekend. Nor am I having any luck finding this elsewhere, including at Beach Camera.
Where to try next?
I am half-tempted to machine a replacement out of aluminum, and have one that will outlast the tripod itself by several centuries, but I have other things to do this weekend, and once you start on machining something like this, it always takes longer than you thought.