I have no idea about Technic, but by default I see greatwoods and silverwoods in Twilight Forest. Easiest way to be sure is make a test world and fly around TW in creative. They spawn fairly often, so you shouldn't have to go too far.
Edit: I read it as the trees, rather than the saplings. My favourite technique is just chopping down trees, relevant enchants (like luck) I can't confirm if they affect drop rates, but they quite probably do. In any case, you get quite alot of sapling drops. (nothing compared to normal trees, true, but alot considering the value of the trees)