It would be great if the records were made public. The information may not exist; may be buried in the archieves or will not be made available under the legistlation your citing.
Start with one Force and have a face to face meeting. Show them the records you have and give an explaination for the request. I sure they're reasonable folks.
A M Stevens has a lot of info. have you contacted him. He's been at this a long time and been building a data base. His website is index.htm. I'm certain he'd be willing to share info.
I've been told by a few folks that between 60 and 70% were destroyed. Early on in the disposal program these were sold to clubs and other Gov't organizations. UKPolice Forces obsoleted the Enforcer in the mid 1980's to be replaced by the M85.
If you have an Enforcer (#395) like the one Robert has you're very fortunate. It appears to be genuine. It's missing a few things however he's in the process of acquiring them.
Great rifle, Enjoy
Ron