Which rubber bands am I allowed to use for competitions?

Am I allowed to use any rubber bands or am I required to use a specific Vex one?

If I’m required to use a specific Vex one, can someone link me to it?

You do not have to purchase them from VEX, but they must be the same specifications that VEX sells.

So, you can use any brand rubber band that you choose as long as they are #32 3" x 1/8" or #64 3.5" x 1/4"

VEX’s rubber bands are Alliance brand latex free, from the “strethciness” characteristics I would say they are pretty much the same as Alliance Sterling brand (premium type on Robosource).
#32: http://www.uline.com/Product/Detail/S-15807/Rubber-Bands/32-Latex-Free-Rubber-Bands-3-x-1-8
#64: http://www.uline.com/Product/Detail/S-15810/Rubber-Bands/64-Latex-Free-Rubber-Bands-3-1-2-x-1-4

And you can use any type in size #32 or #64 as long as they are pretty similar:
https://vexforum.com/t/answered-clarification-on-r7-b-and-rubber-bands/29908/1

As a side note, we have a couple different types of rubber bands available here.