There are many sources for glass plates, both new and vintage. I have about ten or more vintage plates right now that I bought for about $10 or less each.
As for the light farm, it is a very good resource for information up to about 1865. I am of the opinion that the texts do not give enough information on how to make the transition at that time and more recently and also that too much reliance is made on the work of Woody Thomas (Woodlief Thomas), who was NOT an emulsion maker, but rather an editor. I knew Woody personally, and he was a great process engineer, but not an emulsion chemist or product engineer.
One has to be careful, without criticizing Denise, to avoid the problems with publishing emulsions at that time. Kodak kept a tight reign on what could be published in the emulsion arena, and Grant Haist has complained to me bitterly about the editing done to the formula that he published for a lith emulsion.
The ward here is Emasculation! Sorry!
Denise is dong a good job, but only with what she can read in the published literature. That ties here hands in a sense.