Hi, the price letter plates are nowadays I would be surprised if anyone sells spares.
Your best bet is to take all the measurements of your letter plate (overall, aperture/hole size, distance between the fixing bolts) and go to a local ironmonger for a replacement. I would suggest look online but it is unlikely all the details you need would be there, ditto with large DIY stores as the staff seldom have the knowledge and are unlikely to open blister-packed products to check
ironmongeryshoponline, October 2009