Where is a good place to get used CDs for your garden for free to deter. Birds and pests ?
Free reuse recycle green gardening freecycle
Try the local public library. Or perhaps places like 'The Bower' and 'Reverse Garbage' in Marrickville.
A twice a year opportunity (more if you walk a little further) comes if your Council has 'Clean-up' days for residents to put out their unwanted items. These days boxes of CDs are put out (and subsequently head off to land fill sites) so if you have a walk around your neighbourhood you are likely to find as many as you want.
Remember you did want them for your garden (not your music collection).
I have stacks which I am willing to donate