Go to google
Click shopping
type windows server 2003
then chose the top link, it links to several competitors, but they all appears to be selling server2003 premium and the likes
I assume this is what you are looking for?
Any reason you want it over server2011 or server 2008?
The software is going on old servers so spending £500-£600 on each license on each machine is no really economically sound. Looking for Server 2003 SBS or Standard.
If its eval you can get it w/o a technet sub. Atleast I downloaded 2008 R2 for a 180 day trial the other day