No books, but I am somewhat in this category as well. Actually, I'm trying to sell a dropshipping site as well. $5,000 obo, but that's a different category.
I've gotten into it a little as well. And quite actually, the site I am selling is how I got started. I bought it from someone else. I, like you, kept trying to find books and everything on it. So many supposed wholesale sites are dead ends, and books are only money makers for the authors.
I will say that it was light years of learning once I bought the site, compared to what information I could actually find. It's a little different when you are calling the shots compared to dreaming about it. Granted, my site is very small with only a handful of orders a month, but it helped me figure out the business along with determing how much time I want to put into it.
Not sure what you are thinking or how far along you are, but sometimes diving in small can help more.
Anyway, if you have any specific questions, I can try to help as best I can. Obviously, not suppliers because that is where the value typically is.