(New player) How to get characters not on current banners as f2p?

Hello, I'm new to the game and I won't spend money on it. I'm a huge Sanji fan and I got every Sanji unit except for Egghead, Onigashima, and post-ts Sanji. I do play the game for fun and because I want to collect all the Sanjis. Currently, I main Royal Wedding Sanji and leveled him up to 61 for now. My priority as a Sanji fan is Oni Sanji first (cuz it's my favorite) then Egghead, and finally 2 Years Later/Cook last.

How do I grind for Oni Sanji as an f2p? Will he have a rerun?