Thanks everyone. I did a Google search and found that 24V contactors are used in air conditioners. I called my supplier again and he found one for me. He also asked about a relay, but I'm not very familiar with relays.
AC contractors call the contactors with a 24v transformers "fan centers" I ofen use them to control special circuits which require low voltage control. Relays are 12 amp or better. They mount on a 1900 box and seperate low from high. Robert
Just a suggestion. Your LV source may not have enough va to energize a LV contactor coil. I would suggest that you incorporate an interposing relay of which its coil, 24vac for example, will function easily with your LV source. When it is energized it would close a contact that would energize the 120v coil which controls the chime. Also, you wouldn't be plagued with a voltage drop between the bell transformer and a contactor with a LV coil. The coil of a small interposing relay would draw very little current and be controled by a conventional door bell switch. Otherwise, a convertional doorbell switch may not be able to handle the LV current required to pull in and hold a common contactor. I believe there would be a much less trouble using an interposing relay. This is intended to think outside the box a bit.