I guess you have the square fob like I used to have. The buttons are crap so is the stappy thing. The only spares on ebay are empty cases and rubber buttons that cost the price of your average liver as they are not in production anymore.
Best thing is to give the chap at abaqus alarms a call. if you have the code card you can reprogram a new fob easy enough i believe ( a round one) or if you don't have the code , remove the alarm ecu behind the stereo carpet an post to abaqus will be back in 48hrs with a new key card and two new round plippers for £99. Took me a while to get around the £99 part but was very impressed with the servoce and the round plippers are much much less trouble.