Glad you asked and I hope someone can help. Onestepahead.com used to sell clip fans but I haven't seen them on their site in awhile now. I actually want to get one also for our upcoming trips to attach to our Mac Quest. You will love your Ray Shade. It helps sooooooo much! But the fan would be a really nice extra!
When we went last July we ended up buying one of the cool mist fans they had at the Mark and would spray DS every once in awhile (he was 9 months at the time). It helped but I'm sure it would have been nicer to just have a clip fan.