Yes, they are readily available. At the first hint of rain, every vendor and shop will have them. We took our own (Totes brand that came from KMart), they were about $4 for kids size and $5 for adult. I think that is about the same price as the one's at Disney (the ponchos seem to one thing they don't mark up so much....I guess they make up for it in volume!). The advantages of bringing your own is that if you choose a color other than yellow, you'll stand out in a crowd (in case your party gets separated) and if you already own ponchos. you won't have to buy another one for everyone. The advantages of buying them at the park is that until the first day it rains, you don't have to carry the poncho around with you all day. I've also heard that if your Mickey poncho gets torn, you can just take it to any of the vendors and get a free replacement.