The seals for +1 seem to drop from Abyssea NMs. I'm unsure of the difficulty, but it seems just repeatedly killing some specific NMs. Last I'd checked, there was no word on the items required for the +2 upgrades.

These updates are pretty amazing, and I wouldn't have quit if my linkshell hadn't started sucking so much or if I'd managed to find a solid Abyssea linkshell, but I'd just gotten sick of doing nothing but logging in and grinding merits in Abyssea. They should have done this stuff two years ago.