Metal halide is still around just harder to find. The only new reflectors still in the game currently that I can think of are Geissman (a custom order direct from them (shipping is a killer I hear) but a fantastic looking and high quality light) and ReefBrite (more traditional looking but the fixture is designed to not get as “hot” to the touch). Otherwise you’re looking at used fixtures (not necessarily bad but may require cleaning, new bulbs, etc).
Bulbs are also still around. I believe the XM has been discontinued. However some vendors, such as Aquarium Specialty still carry Radium and other brands. A newer start up company, AquaBright Solutions -
AQUA BRIGHT SOLUTIONS if I recall correctly is ran by Dave (and another person) from Hamilton and their bulbs should be the same as the former Hamilton bulbs.