I was under the impression that you already owned the lamps. If not, why not use LEDs? They're safer, cooler, last longer and require far less power. Halogen lamps are really nothing but heaters that make a little light (≈5% efficient for lighting).
PWM is the preferred method for dimming, but this is the first you've mentioned the need for anything more than an ON/OFF arrangement. Do you have any other design requirements you haven't mentioned?
If you're looking for a fire simulation, try searching for Halloween, DJ and theatrical special effects lighting devices. There are plenty available, already designed and tested, ready for sale.