Here are some suppliers and sources of undyed yarns and spinning fibres
Meet the Maker – Sionnach Yarns - Baaad Anna's Yarn Store
spinning – Ceulan Fibres
Journal – Jan Atherton
Breed Study :: Coopworth – Wool n' Spinning
School of SweetGeorgia Kits & Projects - SweetGeorgia Yarns
School of SweetGeorgia
SheepSoft DK by ByLaxtons, British Wool
Why is hand dyed yarn always merino wool? : r/YarnAddicts
Sweetgeorgia Yarn - Canada