Here is the skinny since my SC primer disappeared and I haven't had the time to rewrite it..
The MPC01 is the light/siren controller for the BLINK and SC (aka serial) lightbars and componets. It will control the BL10000 and SC series bars and any componets that have BL in the model number: BL627 (100/200 watt siren amp), BL2150 headlight flasher, BL (or ISP) 94 strobe power supplies, etc. The "F" revision or better supports the SC series bars (Ultra SC, Liberty SC, Patriot SC).
The MPC02 is the same, but only feature light controls. No siren functions.
Both the MPC01 and MPC02 REQUIRES the Whelen Transporter interface box to program. All light and siren functions are programmed into the box. Plugging a BL627 into a MPC01 does not guarentee that all the siren functions will work "out of the box" as some of the siren functions may not have been programmed or programmed differently.
The MPC03 is the Cencom looking head and only requires the software and a USB cable to work. The transporter is not used.
In terms of finding equipment...its feast/famine. BL627's typically go for 75-100 on ebay and controllers run around $100 or so as well. Shop around.