Use the following to make a determination if a software product is a sole source. This information is provided by Gartner.
These are the sites we were using to check the sole source. Capterra is the one that was very useful. You basically search by functionality and away you go…
All of these sites are owned by Gartner and can be used.
All of these are free to use – even the chat assistants who will do research for you!