Appart from official distributor Newark/Farnell : http://www.newark.com/jsp/bespoke/bespoke7.jsp?bespokepage=newark/en_US/landing/raspberry-pi/rasp-pi-accessories.jsp&et_cid=22877260&et_rid=3535947&Linkid=New-XBMC-Bundle-&CMP=EMC-22877260
This website is also interesting: http://thepihut.com/