Hi everyone, I'm pretty new to the game and I have a question about collabs

Hi everyone, I'm pretty new to the game and I have a question about collaborations.

I have Rumi Cookie at 4 stars and I'd really like to promote her to 5 stars. Now that the KPop Demon Hunters banner is over, is there any way to still obtain her Soulstones?

Also, do universal / wildcard soulstones exist (that work for any cookie)? Or is there any shop where I can buy Soulstones for cookies I already own, including collaboration cookies?

Any help or tips would be really appreciated! Thanks in advance