Is there any place in Ottawa that sells used mac parts cheap? Extremely limited income.

Can you be more specific as to which used mac parts you are looking for.  Some of us may have those parts looking for a new home.

Memory, battery and power supply/power cord for a macbook. Mouse and keyboard for a G4 Digital Audio.

You need to be more specific about which macbook you have.  If it is running, click on the apple then on About this mac.  If it is not running, look for information on a label on the bottom.
As for the mouse and keyboard, I have an old PowerPC G4 (AGP Graphics) and have used various PC-intended USB mice and keyboards over the years.  I'm currently using an older Logitech Cordless Navigator Duo for input.

The macbook is not running. There are no lables on the bottom or inside the battery cavity. From looking at manuals on the apple site, it looks identical to a macbook 13" early 2008.

Make that no labels. Silly you can't edit posts.