Hey. There are many 8 bit vst out there. google Tweakbench. They have many freeware vst that you can use in Fl Studio. Tweakbench has a drum synth that is easy to use inside of fl. If you can find Unknown 64 it has some drum presets. And you can make all sorts of sounds with YMVST My personal favorite is Basic 64. Good luck
http://www.delamancha.co.uk/basic.htm
Available at the link above is basic 64. Magical 8 Bit is good. and ymvst is good too. If you have any questions feel free to ask.
http://www.ymck.net/english/download/index.html M8B
http://www.preromanbritain.com/ymvst/index.html YMVST