Create a 3x5 taming pen at least 3 walls high with wooden ramps at one end. While on a flyer, gain aggro and lead the Allosauraus up the ramp and into the taming pen. Then Tranq away.
If you can kill off the two weaker Allosauraus in the pack that you do not wish to tame then do so, it will make this method easier to perform. The easiest way to kill the other two is with a long neck rifle from the back of a Quetzal platform saddle.
Try to make them fall into a ravine. Flyers help with this tactic. Or better, look for some that spawned or fell into one. There’s a ravine on my SP game where there are around 11 allos that fell into it. After getting them into a ravine, kill off all but the one you’d like to tame. Proceed in taming as usual.