Is it the key or the transponder around the ignition switch barrel ?
If it's the key you can try taking the chip out of the key and gluing it close to the transponder ring, or actually onto the outside of the key _as long as you make plans to replace it_ (it won't last long like that)
I've seen security over-ride boxes which claim to be able to disable the imobiliser system, which would have you up and running again soon, can buy them on eBay. You need to look at the manual to see what name they call the security system 'cos I've forgotten, it's 4 letters long IIRC, then look on ebay for that name and voila you should find something that can help.
Chris Barron email@example.com