My info is about 8 yrs old so may well be wrong now, but I can see two ways of fairly reliably getting onto fires if you're willing to invest several years.
One is to go fly for Papillon on the south rim of the Grand Canyon. Of course their core business is tours but they had several aircraft on fire contracts each season and their number kept increasing each year. They hire several new pilots each year - minimums were 1,000 hrs PIC back then. Make it clear that you're there for the long haul (most young pilots leave as soon as they get some hours because there isn't much to do in the area and flying tours gets boring) and want to get into contract flying, then keep your mouth shut and work hard - they really try and look after and hold onto good people. You'll fly tours for two years and probably start getting some contract work (animal counts and so on) in your third year, and some fire work one or two years later. Just remember that tours will still be their core business and outside of fire season you'll still be flying tours.
The other is going to Columbia (or one of the other logging companies operating two-crew aircraft such as S-61s or S-64s) as co-pilot; they all have some aircraft on fire contracts during the season and eventually you'll be on one of them. Just remember that their core business is logging and you'll be doing more of that than flying on fires - and there is a reason why the turnover for logging co-pilots is as high as it is.
Good luck, if you really want to fly on fires and are willing to make the necessary sacrifices then eventually you will succeed.