I'm in the process of setting one up with a few other parents. We will be an official ptsa that will be at the district level, so 1 special needs ptsa for all the schools in our district. We'll gave similar rules and bilaws to the traditional pta's/pta's in the district. We are modelling ourselves after another sn ptsa in a neighboring district, so far they have been great mentors.
I'm the president for my youngest son's elementary school PTA. We really donot have a special needs PTA. Wish we did. We do have a Special Education Liason (which is me). I too would like to know how a special needs PTA/PTSA works.