Barrel Depot makes a barrel especially for this kit. It is barrel number 53002.
Yes, the M48H is a conglomeration of the Academy M60A1 hull and Academy M48A5 turret along with AFV Club M88 tracks and M88 road wheels. There are supposed to be a couple of sprues AFV Club made for this kit specifically as well.
Sprue Z has the gun tube, sprockets, final drives, air cleaners grenade launchers, mantlet and turret ring. This sprue is specifically labeled AF 35S-01 M48H. Sprue W contains the .50 cal machine gun and the M240 loader machine gun.
The Academy M48A5 sprues is sprue B and contains turret details like the search light, cupolas, etc. Academy M60A1 sprues B and C contain parts to detail the M60 hull.
If you're missing the barrel, you're probably missing the whole AFV sprue Z.