collab with artists who are the same size or smaller than you and just keep posting your work on multiple websites and tagging it. there are all kinds of videos on youtube you could find about how to market yourself, get seen, tutorials on how to make specific styles that might be popular and draw more views, etc. you can go anywhere with it. but yeah if youre not hearing back from the people you are messaging to collab with, try and find some mutual followers that are basically your friends that you can collab with and do a lot of those with a lot of different people, and you will learn a whole lot as you do it