Not sure about writing, but if you want to get into drawing that kind of stuff you just open a Twitter/Deviantart/Tumblr, post non-commission work initially until you have a bit of a following and people asking to commission you will come themselves eventually. I worked that field for about half a year while I had nothing to do because I dropped out of college, and in that time got up to like 100k followers and a solid 400$ a month without advertising it much. I probably could have squeezed out more if I tried, but I didn’t really feel like it haha