So sorry :( we have excessive wait lists for services in our area too.

One thing we do with our kids is when they get upset is get them to breathe. When they were about 1-2ish and tantrum we would bear hug and take deep breaths and hug them with our breathing. (So like squeeze on the inhale) Our oldest is almost 4 now and when he’s getting mad and upset we ask him to show us how he can breathe. (Sometimes we need to ask a couple times 😅) He will take a few deep breaths and then we ask him to be calm and to use his words to tell us what’s wrong. Our oldest’s knee jerk reaction when he’s upset is to start throwing things (anything within his reach is fair game, food/toys/shoes etc.) so we always try to head him off with the breathing reminder before things start flying. Our youngest is 2 and he still requires the whole bear hug process, hoping he catches on too but man he’s a stubborn one. His tantrums are more self-injury though (like throwing himself on the floor etc.) and he’s not so much safety risk to those around him.

Remember, to an ASD individual, anything challenging is at least 3 times harder.
The Speciality teachers have to learn your child as they go. They don't have immediate answers either. They are taught a certain way of teaching that's more factual, the rest is up to them to learn.