I know of a couple of options.
First, head to the electrical conduit section for these parts (I happen to have the Home Depot parts but probably available anywhere)
Halex 1/2 clamp connector Home Depot 90661 $2.05ea
Halex 1/2"lock nut Home Depot 26190 bag of 6 $.73
Halex/Rigid 3/4-1/2 reducers (washers for thermo clamps)Home Depot26820
Combined they result in this:
Note that if you use a Maverick therm the probe may be too thick to pass through the unaltered rubber gasket that goes inside the pipe. If so, you can just cut one of the walls so the gasket opens into a collar and can wrap around the therm cable.
Another, even simpler option is to just drill a sufficient sized hole to run your cables (1/2" to 1") and use a sheet of magnetic strip to cover the hole. Cut a slit from the edge to the middle of the magnet strip so you can pass the cables through and it'll adhere to the steel drum wrapped tightly around the cables. Then use an uncut magnet strip to just seal the unused hole for cooks you don't happen to use therms.