Need advice on rainbow pets

I really want that rainbow tag, and I couldnt find anyone who would let me borrow their pet (which is i understand bcz wdym 21k at least) so I decided to start making mine but idk where to start, I have a lvl 10 ruby painted bat and a 15 lvl emeralg guinea pig, should I keep building on them? Or find an easy achievable pet? Also is there anything else i need😭? Im anxious about it