Note that "United Nations Convention on Contracts for the International Sale of Goods (1980)" is a Library of Congress subject heading that can be used on TALLONS. Of course, searching by keyword is also possible.
Articles on the CISG can appear in all kinds of law journals. As of April 2020, a keyword search on the name of the Convention returned over 400 results in the Index to Legal Periodicals.
The CISG Advisory Council is a private initiative of international scholars of international sales law. It issues opinions relating to the application and interpretation of the CISG. The opinions would have formally the status of secondary sources, but they have substantial persuasive authority. The opinions can be found at the link given below.
The CISG Advisory Council Opinions by 
UN Convention on Contracts for the International Sale of Goods (CISG): Commentary (2nd ed.) by 
Commentary on the UN Convention on the International Sale of Goods (CISG) (5th ed.) by 
Honnold's Uniform Law for International Sales under the 1980 United Nations Convention (5th ed.) by 
The UN Convention on Contracts for the International Sale of Goods: Theory and Practice (2nd ed.) by 
International Sales Law - CISG in a Nutshell (3rd ed.) by 
Understanding the CISG: a Compact Guide to the 1980 United Nations Convention on Contracts for the International Sale of Goods by 
CISG Basics: a Guide to International Sales Law by