MEC has neck tubes on sale, and when I was at Costco in December, they had "Bula" balaclavas. If they still have them, check the size - I bought an XL and it was the right size for me.
For those of you who are lucky enough to have a Grandma who loves to sew - bandanas are pretty easy to make with some fleece and Velcro. The Jones gang are equipped with bandanas made by Gail's Mom.
The ones in my collection are 21" to 23" on the longest edge.