Hi Cullen,
I believe you can use the Function modules from CL_FRONTEND_SERVICES. They offer many methods for directories and file manipulation and file processing as well.
Also, there' a good article here about working with files. You might want to visit this one:
Working with files - ABAP Development - SCN Wiki
There's a heading title here that says getting the list of files in directory. It might work the same for finding the directories given a file location parameter.
Hope this helps.
Thanks and warmest regards,
Ryann Ong