I had a similar problem - not at your scale, though. I'm hoping to resume running a Secrets of the Anceints campaign. As it is set in Regina sub-sector, Spinward Marches, I got a friend to photocopy the Regina sub-sector page as an A3 page.
How is this relevant? Simple. Photocopy the blank subsector at the back of the Core Rule Book ( or print the blank subsector map from http://www.mongoosepublishing.com/rpgs/traveller/core-rulebooks-accessories/traveller-core-rulebook.html )
Once you have an A4 subsector map, photocopy it again - reducing its size and playing around with it until you've got what you need a suitably sized blank sector map.