To get an overview on which namespaces are declared in a (known or unknown) C# project or solution, you can simple run your favorite grep tool on your source directories:
grep -r "^namespace " * --include=*.cs --exclude-dir=*Test* --exclude=*designer.cs > files-namespaces.txt
Here, the -r switch causes recursive search through all subdirectories, –include names the files to search, –exclude-dir and –exclude the directories and files to exclude from the search. The result is written to a file.
This will produce a list of all namespace declarations.
grep -r "^namespace " * --include=*.cs --exclude-dir=*Test* --exclude=*designer.cs -h | sort | uniq > namespaces.txt