Searching for files is a bit expensive to add to your BigFix client loop. I might suggest you use an Action to perform the search and then relevance to read the results of the search, similar to this post:
Or, if the folders are limited, you could use a plural folder construction.
q: files whose (name of it as lowercase ends with ".cf") of folders ("/etc";"/etc/mail")
Or, since you wanted blah specifically, you can also create a plural file object like this:
q: ((files whose (name of it as lowercase ends with ".cf") of folders ("/etc/mail"));(file "/etc/blah.cf"))