CFDirectory -> increment

Is anyone able to give me a sample script, such that if it finds an existing file, I can create a file with an incremented number.

Not sure exactly how to phrase the question but here's an example:

The following files exist:

file01.dat

file02.dat

file03.dat

I want to now create the next file in sequence based on the existance of the above files:

file04.dat

Can someone provide some sample code as to how can I use cfdirectory to come up with "file04.dat"?

Thanks