how can can i get the code for my rover 414 R reg immobiliser?

after replacing car battery immobiliser has stuck on have replaced battery in fob but to no avail autoelectrician has looked it but needs code i have not got the manual so where would i get this information to get car back on road.as rover no longer in operation we then tried alex noble but there was a problem with their software dont know where to turn. car is a rover 414 R reg 1995 model.