Suppliers of Pigments, Watercolours & Specialist Paper.

Pigments & Watercolours:

UK 
Choosing Keeping is a London based store and stock some ready-made mineral based watercolours. These watercolours are quite coarse (not good for fine rendering work) but the colour and coverage is good. (Exception is the Lapis which is low grade). The sets are linked here. Please note that Choosing Keeping stock some incredibly beautiful Japanese pigment sets which they are advertising as being 'mineral' based. Intrigued by the very bright colours (unusual for natural pigments) I spoke to the store manager and discovered that these are not natural pigments, rather the minerals are manufactured using a combination of natural and synthetic sources which are combined via a machine to synthesis a mineral. The colours (linked here) are beautiful, but please be aware that they (and the others in the Japanese range) are not natural if that's what you are after.
Jacksons sell a range of synthetic and natural (inorganic/earth and mineral) based dry pigments. I have linked them here and here
AJ fitzpatrik  stock Kremer pigments and it is possible to place a Kremer order through them. This removes the cost of international shipping.
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World 
Ready-Made Shell Gold:
 
Pigment Foragers:
You can also buy dry pigments from geologists and/or pigment specialists. Linked are my preferred foragers:

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Paper Suppliers: