When my kids have tantrums, i just stick them in their room until they calm, and then give it 1 min. They've actually stopped having a many tantrums, because they dont like being put in their rooms (they dont have toys in there) Like you, i was at my wits end - a 3.5yo, and a 22mo starting the terrible 2's...

Sorry i dont have more suggestions to help you out - but thats what worked for me.