In spite of the fact that I live in a fairly populous suburban area, I couldn't find this item at any of the DIY hardware type stores and all of the hypothetical estimates sounded unreasonably high.
I got on-line, searched around and found this. It's a great part, at a good price, BUT there is one aspect that you need to pay attention to. There are a number of these on-line that look to be the same. They are not. In my case, I actually ordered the wrong one (which has slightly different physical dimension). However, since 90% of the wear for these is in the O rings, I was able to switch the O rings and solve my problem.
*** Make sure that you specify the correct model ***