If you use a forestry multifarm to make a rubber plantation it will automatically tap the resin spots when available. It won't cut down the trees, but just the rubber you get from the resin should fill up your system very quickly. You could use an arboretum to get logs and saplings, but I prefer to just go for the resin. Much simpler.
Slimes are also pretty decent. I'm about halfway done with my slime soul shard and I think I've gotten something like 20 stacks of rubber from the slimeballs.