I have 2 softer quieter clickers that I have and love. Especially when I'm in places I don't necessarily need everyone to hear the clicking (um, like at an agility trial, hehehe).
So, here are the two I have.
Clik-R: You can slip your finger through the loop so you won't lose it.
Karen Pryor's i-Click: I think it's this one.
I honestly can't say where you can buy them. Both of these that I have someone gave to me. I wonder how much it'd cost to ship one of them to you. I don't use the Clik-R one very much, too bulky. I was thinking, I could record how loud the two are so you can see if they're "quiet" enough. If you want a vid, let me know. I'll do it later tonight.
The Clik-R is available at PetSmart in Canada, that's where we got ours.