You'll be hard pressed to find a carrier selling an unlocked bootloader device from any of the major manufacturers. The bootloader is just one of those you really don't want to mess with on a phone casually. After all, who is going to want to learn how to JTAG their phone and search random forums for the boot image?
Now if you're looking for info on how to SIM Unlock the phone... talk to Verizon. They have to unlock it if you have paid for the phone.