Welcome, Chris!
I have not heard of seperately available heads, unless someone has one from a light with a wrecked tube they want to sell. If your light is CMG, it must be the older (not Gerber) style with the lanyard lug at the tail, twist head to turn on. These CAN be modded with a new LED, but it is not as easy as the new Gerber tail-twist lights. The big problem, after you defeat the crimp edge holding the pill in the head, is that it is potted in epoxy. You have to repeatedly heat the pill and pick out the epoxy until the circuit is exposed. Then there are plenty of good LED's to choose, the most obvious is the Nichia CS U-bin. They are available in singles for $1.50 at the Sandwiche Shoppe, here:
http://theledguy.chainreactionweb.com/index.php?cPath=48_52_77
Or, if you like the new style, the Gerber's are selling for about $15 a lot of places these days. Not as much of a challenge, and doesn't solve your old light problem. Hope this helps some!
