Nearly 3 year old hitting, biting and kicking

Does anyone have any advice? I am really struggling with my nearly 3 year olds behaviour. He mainly does it to me and my husband but if he's out of sorts or in a mood, he does it to other children when we have playdates. If he doesn't get his own way he lashes out. It's so embarrassing when he does it to other children. We have tried everything. We never give in and always hold form on the rules. We've mainly tried to go down the gentle parenting route, although some days this has just not happened because we've simply run out of patience. Does anyone know of any behaviour consultants that could help? Thanks in advance.