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.
They fit through the regular dino gateway, so build a pen 2 walls tall with one gateway on a side, if there’s a group of allos you can either kill them before or after trapping them, if you have a flyer this is a joke, super easy
THE best way to tame anything is to use an argy cage, simply use like 5 dinosaur gateways made of stone and keep one gate door open before you find a dino to tame, once you do, lead it to the cage and then run out through one of the gaps between the gateway frames and obviously close the door and, tadaa, one stuck dino to tame