First, I want to thank everyone for their feedback.
Merlin the Tuna: I insist that spellcasters writing scrolls (and copying into spellbooks) use Magic Ink, similar to what is suggested in 1st edition DMG. There are several recipes, and all include components mundane and rare. So rare, you'd only find them in towns and cities, and vials of prepared Magic Ink would be rarer still (PCs would do an Alchemy check to make Magic Ink, very low DC). I was thinking that one consequence of a party with 2-3 spellcasters making dozens of scrolls would be local spellcasters would get wind of what's happening when the shop runs out ("Master Grimshield, you're out of Dire Squid Ink again?!") or the suppliers decide to raise the price from 50gp a vial to 500 gp.
I'm really not trying to be cruel to the players, just simply trying to have some real world versimillitude...
Another idea I had in mind is someone with multiple scrolls might have a higher DC for finding the right one, shuffling through the thick stack of vellum, or even making sorting through more a dozen is a standard action, or something like that.