Another way I’ve obtained rainbow gems is by breaking space rocks on the board breaker. In one of my saves, I have a teen Sim who has the “make my IF real” opportunity and needs to find a rainbow gem. Her mother has mastered martial arts and the family has already obtained a lot of gems via her skill. The mum did already get a rainbow gem with the board breaker, but she got it cut and it’s being used as house decor. Both her parents also have the Collection Helper lifetime reward too. In any case, the household is already at capacity so I’d have to wait to make the IF real. The teen’s four younger siblings also have IFs... I don’t mind them overall. I’ve only made an IF real twice.