Historically the tanker business has never been predominantly ex-military. The military does have limited fire mission assignments; two MAFFS C-130 units delivering retardant, and a number of helicopters are brought to service doing bucket work, but it's not dominated by military pilots, nor military aircraft.
Many of the aircraft in use are ex-military.
what do they consider to be heavy turbine time
"They" don't, nor is "heavy turbine time" relevant nor important to getting you hired into tankers.
are there any web sites with good info on minimum times and possibly a list of companies that do fly tankers
You might try the Associated AirTanker Pilots at
www.airtanker.com.
Heavy tanker operations are limited now to Aero Union (P-3's), Neptune (P2V-5's and P2V-7's), and Minden (P2V's). The California Department of Forestry flies the S-2 tracker, converted to turbines, as the S-2T. Additionally, AeroFlite operates CL-215 tankers.
A number of single engine air tankers are in use, three times as many as heavy tankers. These are predominantly the Air Tractor AT-802, and the PZL M-18 Dromader. These are largely contracted on a call-when-needed (CWN) basis, to the Bureau of Land Management. They are used interagency as requested.
Job openings are few and far between. Heavy tanker openings don't occur often. Neptune recently had a few, but don't hold your breath. CDF has a very long and distinguished waiting list with experienced fire pilots on it. SEAT aircraft generally require considerable heavy tailwheel experience and ag experience, and the proposed changes the government may require will be either a thousand or fifteen hundred hours of ag (crop dusting) experience, among other things.
All you can do is keep knocking down doors and trying. It can't hurt. When openings were more plentiful, it took me eight years of banging down the doors go get my first tanker job, and that was with several thousand hours of flight time, maintenance experience, ag experience, several years of ground firefighting experience and several years of air attack and fire patrol experience. Your mileage may vary.