Try  www.remotealarms.co.uk in England.  they will sell/ rent over ride.. Just plugs into your OB2 port. and you get new programmed key FOB.. cost is $222 USD plus postage.. I  bought one recently . works great..

I have a 1995 Mini Sidewalk edition and the security system has gone bonkers. Any way to disable it? I have tried everything with the fob, new buttons, battery replaced, nothing is happening. It doesn't even respond in any way. It did before the button replacement, but nothing now. Car is a paper weight. I really want the system gone, it's been nothing but aggravation. Any help would be much appreciated. I actually thought about an aftermarket ECM.