Yesterday I heard one of the air tankers from here in TX get sent to LA. They were told to use air-to-air on 122.925 (AM) and air to ground on 167.375 (NFM). I don't know if those frequencies are used statewide or if they were ordered for one particular fire.
Check the FAA TFR page for TFRs for firefighting. They often list a contact frequency.
Watching the planes on adsbexchange.com right now. The tanker is flying out of Alexandria Intl and it is a DC-10 N603AX. It flew from alex intl to the area between Leesville and Oakdale where the spotter planes have been flying. I see a few different spotter planes that keep circling the area:
Two Rockwell Turbo Commanders - N95LF and N425DT
A US Forestry Svc Kingair N147Z
Then there is a LA Dept of Agriculture and Forestry Cessna 182 Turbo N232AF flying between Alexandria and Natchitoches.
Looks like the DC-10 made his drop and is returning to Alex Intl. He flew about 1500 feet the whole way.
Man, if I was out in a rural area on some little back road and I suddenly saw a DC-10 flying 1500 feet over me it would definitely elicit a dubya tee eff reaction if I didn't know what was going on.
Additional edit: Now I see an MD-87 and an Avro RJ-85 which are also tankers.