6 year old with problems at school

My son was diagnosed with high functioning ASD 2 days ago. Sorry I will ramble

He is an a mainstream school and as we are in a small village, it is a small school with mixed classes.  While class numbers are smaller than average in the towns which is beneficial, the fact that primary 1,2 and 3 are together is not i feel as it has to be confusing with all the kids at diffrent levels. 

He is primary 2. This school also provided his nursery and as a whole we decided to keep him in nursery for an extra year to try to help him be more emotionally ready for school. My daughter has also attended this school since nursery and she is now P7. It has been the same head teacher the whole time along with many of the teacher's and we have a good relationship. Before he went to nursery we had warned them of his emotional and behavioural issues though undiagnosed. They have always tried to be understanding and help him however they could. He has an IEP and they try to use visual aids also. 

The problem recently is that he has become violent towards the other children. I think one P1 irritates him the most and the head teacher did say this child is very loud. However he can't be hitting children at school especially as size wise he is close to a 9/10 year old. 

Lasy year he got on really well with his teacher who is actually a friend of my husband from school.This teacher was exceptionally understanding, put a lot of effort in finding strategies that helped him not boil over. He was much more confident in his abilities and appeared happier than now in general. Part of his IEP was the head teacher would take him out of class to chil out as and when required. 

This year however the school have had to make massive cutbacks and I believe this has affected my son badly. Partly because the school could not keep the brill teacher on a they did not have the funding for a full time memeber of staff and she needed that. I know the head teacher really faught for the funding for this teacher to stay. Now cut backs are so bad that the head teacher has to teach my son's class 2 days a week therefore there is nobody to take him out to chill out. I also believe that during playtimes there is not someone understanding around and he just keeps getting sent in as the janitor watches the kids. The fact he is being sent in cannot help with his social interactions. 

Anyway my question is how do I go about getting the extra help he needs at school, extra funding perhaps for an 1:1 assistant.. Just anything to help him be happier at school. He is not struggling with the work but when he is anxious/unhappy in general he loses confidence in his ability to do the work.