You can
buy the whole push button switch on eBay for $12.95 + $.50 S/H.
NEW ProVape, ProVari & ProVari Mini V1, V2 & V2.5 Replacement Push Button Switch | eBay
Or...use a bead as a replacement button. There are cylinder shaped beads in a variety of materials (ie. plastic, stone, glass, etc.) as well as many diameters and lengths. They have a hole in them already, so it should be easy to attach one with the proper jewelry type of glue. I just measured the button on one of my 2.5 Provaris and it's a 6mm diameter button. Cylinder beads do come in 6mm diameter, too! Would just need to either know the length needed and get 1 that size or be able to shorten it if required. I make jewelry as a hobby and have various cylinder shaped beads. I'd send you a couple different ones free, if you'd like me to.