You can get new Deore level rear derailers. Microshift’s Advent is another option for new derailers. Alternatively there are tons and tons of used 9 speed derailers out there even up to XTR level that are relatively cheap. If you have a co-op nearby, I bet you can find dozens of them. At both co-ops where I volunteer, we throw away the lowest rear derailers and keep the high level ones because we have so many. I, personally, haven’t bought a new 9 speed derailer in the last 20 years because I have access to so many.