Using Automator to filter out every third file?

[seenew]

I have 4,500 images and I'd like to pull every third image and put them in a separate folder. The files are numbered, so I'd like to get 0003, 0006, 0009, ...etc.

Any ideas?

They are bracketed exposures for an HDR time lapse, so they have exposure bias attached in their metadata (+1, 0, -1) but I can't figure out how to sort by that info in Finder, Bridge, or anything else...

Thanks!