This is absolutely the best place to get a Calaham ABR-1 bridge.
http://www.callahamguitars.com/index.html
Are you thinking something crazy like someone has one just hangin' around they don't need. I have used the Callaham ABR-1 bridge on about 5 or 6 builds and love em'. If I had an extra, I would be saving it for a future need... Bite the bullet and get the best from the best!
The really great thing about getting parts from Bill is that if he does not have the part you need, he will custom build it for you. Yes, that type of service does come with a premium charge, but you won't find better parts...
Regardless, :rock-on: and good luck!