Just look on the Ringtones board of this community! Or search the web for pages that sell tones and use the preview option on these pages, most of them also use .midis for previews so you can just copy them to your PC!
www.2thumbswap.com COMPLETLY FREE... they send them to you sms too. so it is possible to get them on the nokia 3560.. but there servers are always busy.
I know it's not free but there is just a one time donation of $5.99. www.3gupload.com is what I use for my 3560. I just use the WAP and download ringtones directly to my phone, same with wallpapers. I probably downloaded over 50 ringtones so far with it.