Does anyone know where to get the feelies for older interactive fiction, or decent copies of them online? I'd love to play something like Zork or Hitchhiker's Guide, but would rather not rely upon walkthroughs unless I had to. Thanks!

Im not sure what you mean by feelies ... but if you don't mind emulators and roms http://www.virtualapple.org/ has a web based emulator and a downloadable one and has all the old text based Zork games. If I remember right the Zork games got abandond or released to the public not sure which so this might even be legal.

Sorry for my ignorance but... what are "feelies"?

Oops, sorry! Feelies were physical goodies that came with the game. For instance, with the Hitchhiker's Guide to the Galaxy, it came with a "Microscopic Space Fleet" (in a sealed plastic baggie), the orders for the demolition of Arthur Dent's house, and the orders for the demolition of Earth.
On the one hand, they were just neat little doo-dads meant to draw you into the game (like many of the prizes that come with collector's and special editions of games today), but more importantly, they functioned as a primitive (but clever!) form of copy protection, with the feelies containing information that was critical to solving some of the game's puzzles.
As such, games that used feelies in that way would be pretty much unbeatable unless you used a walkthrough--which I'm sure I would need for a game like Zork (I've tried it before and it's pretty mind-boggling), but I'd like to give myself a fighting chance.