Silverwood trees apparently purify the area around them, and have their own aura nodes. It seems like a no-brainer to plant a couple of them around my base to offset the damage my inept thaumaturgical tinkering is doing.
However, I haven't been able to get any silverwood saplings at all. The Thaumonomicon has this to say:
a silverwood sapling [is] a prize beyond measure.
So I assume it's not as easy as cutting down silverwood trees. Doing that yields nothing at all, aside from the wood.
Is there something special I have to do to get these saplings, or is it even possible at all? I know the saplings exist as items, but that could just be for server ops to spawn in.