Another +1 for Shepard Air--just had to retake it after my previous results expired since apparently your results CAN expire, even if you're flying for a 121 carrier actively, for the purposes of doing an ATP checkride outside of a 121 training program.
Why don't you already have it, might I ask, if you have an ALPA sticker as your avatar and it says you're a FO? I've always assumed all 121 co's req. it as a prereq for hiring--guess I was wrong...