I guess the 100mm+ reflector is used on one of these big reflector spotlight mentioned around here before, maybe you can just order the whole light and mod it from there.
http://item.taobao.com/item.htm?spm=2013.1.0.0.z2jl3n&scm=1007.10009.257.0&id=17178079954
EDIT: A review thread found here .