Sorry, that reply was to the OP.
I agree there is very little support out there. My DS was diagnosed with ASD and ADHD at 4 and is now over 18. We have been through the mill along the way including DS being excluded from school for things which were entirely to do with his additional needs.and tbh the most useful support we have received is the Mencap support. We accessed it through the young peoples employment team at the local council but it took a bit of pushing.
DS has pretty much always had a statement and now an EHCP, but they mean very little in real terms.
One other thing we tried which worked well was a voluntary job in an Oxfam bookshop for two hours in an evening twice a week. The people there were lovely and very inclusive and appeared to have a good understanding of SEND. They let him work behind the scenes in a quiet environment sorting and pricing books and he worked there for about six months.
@Punxsutawney my DS is also pretty much totally isolated, but I am not sure it bothers him that much. Along the way there have been a couple of boys who were also on the spectrum who would have been friends but he really could not be bothered to sustain an engagement with the even with me and their mums facilitating.
I do worry terribly about what will happened to DS when I am gone as he is a very vulnerable adult. My attention atm is focussed n trying to get him PIP, but as he is reasonably intelligent and articulate I suspect we will fail.
What they will not see of course is that he can be influenced by anybody, has no idea of the value of money, though he likes shopping, and is absolutely ripe for exploitation. If he was living somewhere and say there was a water leak or the fuses blew, he would simply live with it and would not be able to even begin how to work out how to find someone to get them mended.