[Let's Go] Where can I find Moon stone ASAP right after My Moon?

So I ran out from the cave of My room and into the next city.. then realized I didn't pick up a moon stone..
What is the closest one I can get next or is there a way head back to my moon ASAP?? Thank you!! (Pokemon Let's go)

Unfortunately, Moon stones can only be found in Mt.Moon. The earliest you can recollect it is after you complete the S.S. Anne and get Cut. Traverse through Diglett's Cave and go back via Pewter City. The Moon stone will be in one of the craters, indicated by your partner's tail wiggling. It respawns everyday.

Ditto above. Acquire Cut from S.S. Anne and then brave Diglett Cave that takes you back to Pewter from which you can enter Mount Moon via Route 3. Since Moon Stone respawns, you won't have to worry about running out.