A couple of very useful books:
"The Artist’s Handbook of Materials and Techniques" by Ralph Mayer -I really enjoy Mayer’s Handbook and have often thought of following his recipes for doing small frescos. It is an intriguing idea.
"LEONARDO on Painting" edited by Martin Kemp. Although not about ancient processes this book is a treasure box of commentaries that any painter today could use . . . “an invaluable reference work for art historians as well as for anyone interested in the mind and methods of one of the world’s greatest creative geniuses.”
Ready made materials:
R&F Handmade Paints specializes in the manufacture of encaustic paint
Cuni Encaustics specializing in water soluable cold wax paint.
Make your own paint:
Douglas and Sturgess (San Francisco) – source for ingredients for vegan gesso as well as a source for pigments, binders and wax.
Kramer pigments (New York City) – rare and hard to find pigments as well as binders for making your own watercolor paints.
Sinopia (San Francisco) – rare and hard to find pigments.
Many art supply stores carry dry pigments. You can also order them online. Jerry's Artorama has great prices.
Pure beeswax can be found in art supply stores and hobby & craft stores.
Wheat paste - check art supply stores and hobby & craft stores.