The requirements are ATP and TS security clearance.
Go to www.usajobs.gov and then click on "job search" then underneath select "series search" and then scroll down to "2181 pilot". It is tricky to find because it is listed alphabetically, but it falls between "aircraft ordnance" and "aircraft pneudralic," so really it should be "aircraft pilot." Most of the jobs that come up are GS flying jobs for the army and air force, but the FAA ones will come up here if they are available, CBP and US dept of agriculture, and US Forest Service will come up. Right now they didn't have anything available but keep checking back every couple of weeks. Goodluck