I don’t and have never read a J2 fic, but I’ll try and help anyway. Is it any of these? (for future reference, I googled “j2 fic dallas cowboys”)

1st & 10: He Did it Again |  NC-17 | Summary: Jared is the hottest young quarterback to come down the line in a long time. Jensen is the trainer that wants to make sure Jared takes over for the Dallas Cowboys…but then all hell breaks loose and neither man is ready for it…

QB ‘Verse | NC-17 | Summary: Jensen Ackles is the quarterback of the Dallas Cowboys. Jared Padalecki is a newly drafted receiver on the team. With Welling on the injured list, Padalecki steps up to play, but there’s some tension on and off the field.

Next Man Up | NC-17 | Summary: Armed with strength, size and instinctive talent, Jared Padalecki is the first round draft pick for the faltering Dallas Cowboys. Quickly granted a multi-million dollar contract and heralded as the hopeful future franchise quarterback, Jared is thrilled to be a part of the team he grew up idolizing and is all too eager to take the next step in what should be a long and promising career. However, Jared soon realizes he has a much tougher road ahead than anticipated when he meets the prickly Jensen Ackles, the team’s veteran QB and Jared’s number one competitor for the starting roster spot. In a league ruled by money, celebrity and ego, where the roster changes week to week and injuries aren’t so much a risk as a fact of life, Jared must prove himself capable of leading one of the NFL’s most glamorous and controversial teams back to glory. And in the process, must deal with his teammates’ potentially career-ending secrets and his own burgeoning, confusing relationship with Ackles.

If none of those are any good, apologies. Maybe try spnstoryfinders?