See the section on societies and the section on how to get started. The main periodicals are Bank Note Reporter and the IBNS Journal. The SPMC and LANSA have periodicals, too.
For Green Sheets, you can
contact:
The Currency Dealer Newsletter
P.O. Box 7939
Torrance, CA 90504
USA
+1 310 515-7369
1 yr subscription = $44
2 yr subscription = $78