I PM'd you a link but I guess you don't bother with PM's.http://www.futurlec.com/Gas_Sensors.shtml
the bottom one, complete unit runs $9.90 for 1, $7.90 for 100+
my highlights, if you don't see the right type then check the page above.
Gas Leak Alarm Module
Complete Gas Leak Alarm Module for use in Home or Factory to warn of leaking LPG, Natural Gas or Coal Gas. This unit provides output LED and buzzer driver for visual and audio indication when the gas concentrations reaches a dangerous level. The unit can also drive a valve in the gas supply, to switch off the gas if a leak is detected.
The unit requires a 9V DC Supply and is very compact for easy mounting in portable or fixed equipment. Calibration is quite easy and trip point will remain set for the life of the module. This ready to use Gas Leak Module can easily be incorporated into a large unit to provide a full Gas Leak Alarm.
Part Code: GAS_ALARM_MODULE
Ready-to-Run No Additional Circuitry Required
Ideal for use in Alarm Units for Home or Factory
Detects LPG, Natural Gas and Coal Gas
Output Available for LED's or Buzzers
Detection Range: 1 - 25% (Leak Gas Level)
Dimensions: 22.3mm Length, 25.4mm Width, 15.2mm Height
Cripes dude, I thought this just -might- be what you were looking for.