It looks like this was made for hot flashes, but I assume it'll work for MS users. They only last for a short time (30 min or so), but I'm assuming that sometimes that's enough to just cool down until one can escape into AC or at least cool down when you're just way too hot.

http://www.hotgirlspearls.com/index.html

It would be much easier to wear than a cooling neck wrap, for me. I have issues with things wrapped around my neck. I have too many sensory issues. They're on Amazon.com, kind of so-so reviews, but it seems like the bad reviews were made my people who expected them to stay cool longer.