for my son, too. He's dysgraphic and probably has dyscalculia. I don't KNOW he has Asperger's - but he certainly has some of the traits...
I worked with him doing increasing number of matching cards to a viewed sequence of symbols and/or letters and/or numbers... Started with like + O and increased one "symbol" at a time and increased complexity (symbols seems easiest, followed by letters, then numbers...)
It sounds like you have a lot of good ideas going already! One thing - (that you're probably already doing) is looking at the (expensive) resources available and reproducing it "at home" for far less cost - AND more targeted towards your son's needs.
Still - a support group of hs'ers of special needs kids in your area might be a good resource for you for information - as they are very used to "making up their own"....
Here's a general hs special needs link that might lead you to more ideas......
http://homeschooling.gomilpitas.com/weblinks/autism.htmBut finding a local group could be even more helpful...
Also here's a link for "paper" type items:
http://www.incompetech.com/beta/plainGraphPaper/It's fun to scroll through and look at the different "formats" you can print out for so many different uses!