Replacement barrel for at44-10 qe long

I've been looking for replacement barrel for my Hatsan at44 class airgun but I would rather noth have it be another hatsan barrel. My gun shows promise of accuracy at time with groups the size of a pinky nail at 35 yards but then a poi shift with happen and then it won't hold groups even after a barrel cleaning. So I was wondering where I could get a barrel made to drop in my gun.





.... This was the only thread I found that talked about airgun barrel threads.