Thanks for the suggestions, guys! But I've seen the small rotary cutters at the scrapbook shops, and I've even looked at the Fiskar deckle shears, and neither are what I'm looking for.
If you remember seeing photos from back in the 50's, I'm sure you've seen a perfectly cut deckle edge. Nice and sharp, with no fraying or torn edges (at least on a new photo!). I'm guessing that most labs in that era had some type of guillotine cutter to make that deckle edge. But I've searched and searched online, and so far I can't find anything like it.
I'm still open for suggestions!