remote central locking key fob

The key fob which operates the remote central locking has stopped working, after I glued up a split in the button cover and replaced the battery. It looks like this

  and I understand that it’s non-standard. Any suggestions about how to replace the key fobs? (The doors lock and unlock on the keys OK)

So a bit of further research (looking at the back of the fob) shows it to be a Cobra 7727 aftermarket system, which now seems to be extinct as far as spares are concerned. I’m guessing that there’s an immmobiliser/alarm lurking somewhere, which I’m reluctant to mess about with. Has anyone replaced one of these or a similar system?

The car will have a factory immoboiliser so the alarm immobiliser may not be wired. I’d take it out if it were mine.

This any good?

http://www.ebay.co.uk/itm/New-Cobra-Car-Alarm-Remote-Fob-Key-Case-with-Buttons-/191582125221?pt=LH_DefaultDomain_3&hash=item2c9b2f3ca5