I’m not at all proud of this. In fact I think it is horrific. But it will do a reasonable job of pulling out the first argument of all the find_package calls in your CMake code.
find . -iname "CMakeLists.txt" -o -iname "*.cmake*" | xargs grep -Eih "^\s*find_package\s*\(" | tr '[:upper:]' '[:lower:]' | sed -e "s/.*find_package.*([^a-z0-9]*\([a-z0-9]*\).*).*/\1/" | sort | uniq