Trying to RP a drug dealer/addict/hitman type character and Great Khans and assorted Fiends not withstanding I can't seem to find a steady supply of chems. Also what skills and little quirks do you think would be fun to throw in?

You will need science to make some chems.

Make your own chems. Also branch out into tribal drugs like the things added by Honest Hearts DLC. Even better if you can get a mod that allows you to have a greater variety of crafting.

My main character is a Great Khan castout/ drug cook. She has survival and science, and is mostly melee to take advantage of the poisons.

Get the drug delivery quest from Diane at Red Rock drug lab, That was a nice rp touch.