There's an aftermarket fascia plate available for the 5srs that allows you to replace the whole unit. There's also a complete kit available which includes all parts needed for the install (aerial adaptor, loom adaptor and fascia plate). There's actually 3 different options, depending on the spec of your OE unit - see http://www.autoleads.co.uk/Cat 1/bmw.html for details.
Let me know if you can't find one locally - we can soon mail one out to you.

Dominic

Cambridge Car Audio
http://www.cambscaraudio.co.uk