http://store.rainbird.com/product/detail/B60020-M.aspx#.U5Y1tPmwJcQ
It's like the one pictured above. I suppose I could buy the whole valve and only replace the diaphragm to start with - good idea. I just really don't want to replace the valve (yet) as the space is very tight already and would be a hassle, or more so than just swapping out the diaphragm.
http://store.rainbird.com/product/detail/B60020-M.aspx#.U5Y1tPmwJcQ