Shadow Chasers was the prototype campaign for d20 Modern. You can find it in the d20 Modern book in it's full format. It's Buffy d20 / Urban Arcana, basically. I actually ordered it from Paizo. I would recommend it for reading if no other reason. It brings lower powered PC's to the table to deal with Hobgoblin mobsters and sorcerous serial killers while wielding rune covered UZI's. Who couldn't love that?
Why is this issue not available as a .pdf document?
If memory serves, when we went to make the PDF, we found that our copies of the digital files were corrupted, and we weren't able to track down a good copy while we still had the rights to convert them into PDF form. (At least, I *think* that's the story on this one...)