The best book I have seen on chains is "Classical Loop-in-Loop
Chains & Their Derivatives by Jean Reist Stark and Josephine Reist
The last I heard, it was out of print but you could get it on E-Bay.
There are some excellent lapidary schools that I know of. One is
near Asheville, NC and the other at Young Harris, Ga. the one in Ga.
has classes from April thru October and has a website with the
classes listed. They usually have classes on chainmaking.
Instruction, room and board are very reasonable. The name of the
school is William Holland School of Lapidary Arts.