My nephew is autistic and I asked my sister-in-law about your request. Here is what she had to say.
http://www.autism-pdd.net/forum/
This is another great forum for parents with autistic kids. Here is some advice I can offer:
First- The sensory issues these kids go through can be very hard especially when they are hygienic issues. Hair cuts are a biggy and many kids have the same issue. I would suggest not using the clippers(the sound)- scissors only and have someone do it that has patience and time.
If you have a friend or family member that cuts hair and is willing and patient it might help to have them come to the house. The strange atmosphere of a salon might be too much.
Second- Don’t plan on doing it all at once. Make it an all day thing or if possible extend it to a second day. This might drive you crazy but it keeps it from being traumatic. Once they seem to be heading to overload then stop. This keeps it from being that scary thing that Mom or Dad holds them down for!
Last- If they will let you hold them do. Just don’t make it too uncomfortable. For some kids you can entertain them with a favorite toy that they can concentrate on.
That is the best I can advise.
Sherri