The American Scotches are pretty robust in nicotine--Rooster might be a good one. FUBAR, if memory serves, is also fairly high-test.
If you like mentholated snuff, Hedges L260 (my favorite!) is stern stuff, but it's tricky taking a big enough pinch to ge a big Vitamin N hit.
NTSU (an African brand) is pretty strong, but has too strong an ammonia note for my tastes.