Board Thread:Questions and Answers/@comment-64.222.129.69-20130609222213/@comment-5627887-20130618233857

Rubberwood into a Sawmill gives a 33% chance of sticky resin (in addition to some jungle planks), which can be smelted into rubber on a 1:1 basis until you have enough to craft an extractor and gain 3 rubber per resin. You won't need any rubber to make a sawmill and a method of powering it (I suggest a Steam Engine placed directly facing the Sawmill), however it may take some time to collect iron and other crafting ingredients together to make the necessary items. Your other option is to venture out of the biome in search of IC2 Rubber trees.