Go to the following page and register you details with the manufacturers, and they will know whether the parts are still available or not.
http://www.potterton.co.uk/contact/partInformation.php?type=homeowner
Alternatively try the following suppliers.
http://www.partscenter.co.uk
Enter all of the info asked for and they may list it.
I would like to think you maintenance company are being honest, but some times a little digging helps.
Pat
February 2007