It is possible with just FileMaker if you can locate this folder inside your documents folder. There's a get function: get ( DocumentsPath ) that can be used to get a list of the file names and filepaths to every object inside documents and you could parse this list to isolate those inside your folder.
It is possible to do this with any folder located anywhere in your system if you acquire a plug in with this capability. There are a number of different plug ins that can list folder contents. One, MooPlug, is even a free plug in that can do this.
It is possible to do this with any folder without using a plug in if you create and perform a system script (applescript, batchfile, etc.) that lists the folder contents and FileMaker then imports the resulting text file (Not needed with AppleScript as I think it can put the data directly into a FileMaker field for you).
There are pros and cons to each option but the are able to do what you need here.