I've found a company which does the pagers and they respons to requests about their products, but I can't get them to answer emails regarding buying the stuff or where to buy it

They are based in Taiwan.
http://www.generalsecurity.com.tw/
I've been looking into getting a mobile based pager system (GSM, not Radio transmission) which will interface with the OEM alarm becuase I don't want extra keyfobs and the extra messing around with a replacement system. The GSM modules they do just splice into the factory wiring and take the signals from there so its quite straight foward. If I don't get an email response in the next few weeks I'm going to call them, but I don't understand why they are making it so difficult unless it isn't possible to use it outside of that region.
I'll post back when they get back to me.
Hth,
Stuart.