A tanker company is looking for someone who meets the qualifications, and who is available. Presently there are still a lot of tanker pilots who are qualified who are available.
The big secret is to keep after it; keep pursuing the company. In the morning when the job comes up, it's the person standing in front of the desk, hat in hand and resume on the table, that gets the job.
Air attack experience may help a little, but it isn't really something that makes you competitive. Honestly, having a mechanic certificate would be of more interest, as would hands on experience working on airplanes, and most of all, a willingness to get dirty. Not that tanker pilots do a lot of wrenching any more. But it's worth more to a tanker operator to have a pilot who's not afraid to sweat...because you will.
What flying air attack will do for you is give you an introduction to the fire traffic area and fire operations in general. It will give you a chance to operate around others, to make some contacts, get your foot in the door.
Have fun. It beats working, any day.