I've installed valves from refillable butane lighters that I cut down and epoxied into a hole that I drilled into the base of the ThermaCell cartridge. It works great!
There is a company in Thailand that makes odorless mosquito mats for electric repellent units that fit in ThermaCell called ARS MAT12. They also work great, last longer than the ThermaCell mats, and are less expensive than ThermaCell's. ARS MAT 12 are available at the big online auction site or Amazon.
Jim