There are a few different official sets of Copic Markers skin tones numbers, as well as some great bespoke sets you can make yourself.
5 Beginner Copic Marker Mistakes (and how to fix them) — Vanilla Arts Co.
Marker Geek Monday: Copic Basics Part 1
Copic Sketch Skin TONES*NEW* - Arts & Crafts
Copic Markers Skin Tones [Fair and Dark] – BrushWarriors
Copic Markers Skin Tones Numbers Copic Thinking, 52% OFF
Copic Markers Skin Tones Numbers - Copic Thinking
Copic Tutorial - Coloring Skin Tones with Copics
Karen Campbell's weekly Blog. - KAREN CAMPBELL, ARTIST
COPIC markers are versatile double-ended refillable markers with fast-drying, permanent non-toxic ink. The Sketch marker features a comfortable oval barrel with a super brush nib on one end that is perfect for doing professional illustration, fashion design, Manga, and adding detail to your images. The Sketch super brush nib acts like a paintbrush, both in feel and color application. For more control, use the medium broad nib on the opposite end of the marker. Both nibs are replaceable.
Copic Sketch 6-Marker Set Skin Tones 1
Selling some markers: grays and skin tones : r/copic
COPIC sketch マーカー スキントーン - アート用品
Copic 101, all you need to know to get started {creative chick}
Which colors to get next? : r/copic
Understanding Copics and How to get started — Stephanie Han Art
5 Beginner Copic Marker Mistakes (and how to fix them) — Vanilla Arts Co.