DQ Quest - Where to get slime earings

[Madoka]

I have a hunch that they may be a promotional item and are not intended for this event. Perhaps they'll be obtainable with a serial code included with some sort of Dragon Quest product in Japan.

This could be true, 2.3 recently came out I believe, and 3.0 should be coming out soon in Japan as well as the next expansion. or it's already out