I'm not a plumber, so the fact that I have never heard of this brand should not be a huge surprise. I did a Google search on the name "GS Groupo" and got nothing. I will venture a guess that this is something from China and is no longer in business. My best advice, take it or leave it, is to change to a Delta. Delta parts are always available. Buy for a real plumbing shop, not a discount place as the discounters have inferior models. You'll pay a little more, but get a better product. Should not be too difficult to change over, most of the Delta valve is inside the wall and the one you have is mostly outside. This means there won't be a hole in the wall to plug. The Delta is a much more attractive fixture as well.