There are several sources. Reaching out to your VPN vendor is always a good idea. They often have a good feel for the countries in which their services operate and will frequently post guidance on their websites.If you're a US citizen, consider using US State Department resources. The department lists travel advisories for US citizens, and has foreign service officials who can provide general guidance. Check the travel advisories webpage. Your nation's foreign ministry may have a similar service if you're outside the US.To understand which countries ban or discourage VPN usage, NordVPN has a legal guide that lists countries with severe restrictions, bans, and possible penalties for breaking VPN laws.