Is it possible to get sludge bomb on gengar at this point? or do i need to wait for the tm?
Yes, breed a male grimer/muk/gulpin/swalot/koffing/weezing knowing sludge bomb with a female gastly. TMs can be passed down by males through breeding, in insurgence.
Be sure to post this in the correct thread (General / Questions) next time you have a question regarding the game.