Clare Copeley-Williams has the following list of materials she is happy to offer for free together with some assorted underglaze colours that may be of interest.
Talc
Washed wood ash
Whiting
Quartz
Soda felspar
Cornish stone x2
Flint
Aluminium oxide
Molochite x2
Potash feldspar
Colmanite
Bentonite
Located in Shaftesbury, North Dorset, SP7 8AX
Please can people contact me by phone on 01747 858251