For beeswax collage, there are several substrate options available that you can use. You can certainly use Wood, Masonite, Paper, Canvas (small gallery wrapped or canvas panel), Encaustic board, Clay board and Metal.
When painting the wax to your chosen substrate, it is advisable to use natural bristle brush because synthetic brushes will melt. And once you use the brush in the wax, you will not be able to use it again for any other purposes since the wax will harden.
You can buy beeswax over the internet or at craft and hobby stores. When purchasing for beeswax, it can be is sold in one or two pound blocks or in bags that contain small pellets. It can be colored yellow which is natural or it can be white in color- meaning, it's filtered. You can find beeswax online or at a number of craft and hobby stores. Prices will vary but I usually pay around $11.00 for a 1lb block.
Try using this medium now for your mixed media art collage!