Easy to change as previous answer says but you will have to check alignment afterwards.
You can try some online search sites for spares such as:-
http://www.xparts.co.uk/english/request.php
or
http://overture.find-a-part.com/parts_location_quick.asp
You might even get lucky and get a brand new light for less than a spare. I did when mine went!
To protect your lights from future damage you might consider "Light Guards" from Signam. These are plastic covers which fit over the lights. They are expensive and not available for many make/models but are for Primeras. Details:-
Signam Ltd
Harris Road
Warwick
CV34 5FY(Road Map)
Warwickshire
Tel: 01926 417300
Fax: 01926 417333
Internet: www.signam.co.uk
Barry Leggett, February 2007