You can pick up smoking chips at your local hardware or specialty foods store. My local ACE hardware carried Weber Cherry Wood Chunks
, so I got those.
Smoking experts have favorite types of woods for imparting specific flavors upon their meat - apple for a light sweetness, mesquite for a deep penetrating flavor, aromatic alder for a more subtle smoke on fish and seafood, and so on, and so on, but since this is already a bastardized indoor smoking operation I think any type of wood you can find will do just fine.
There isn't anything particularly special about pre-packaged smoking chips - if you live outside of a city and can access some nature that hasn't seen any pesticides, chances are you can collect some wood chips from the world right around you.
Break down the chunks of wood into small chips using a hammer and chisel or a hatchet. If you don't want to mess around with this added step, make sure to get small smoking chips
and not wood chunks
Line the bottom of a heavy roasting pan with the chips and cover them with a rack so that the meat will be suspended above the smoky bed of chips. Then, pour enough water into the bottom of the pan to moisten the chips, but not so much that you cover them. Ideally, soak the chips in the water ahead of time and add in even less water into the bottom of the roasting pan.