re: How do you become part of a collaboration?

As Jennifer has mentioned, you could start your own.
Apart from that, they are generally by invitation. I have checked out your page… and the standard of your work is very good. I couldn’t help but notice, that until today, you haven’t taken time to interact with other cakers or comment on their work.
If you check out a lot of the collabs, you will notice that there is a lot of “caking community” people included. People that are connected to others, not only by their standard of work, but by friendship and respect.
CakesDecor is an amazing place where there is always opportunity to interact, help/ask for help… and generally get to know other cakers at all levels.
Good luck for the future! xxx