go to as big a library as possible, I think you can photocopy that, though you can't buy it, unless they want to sell, but I personally think no librares will want to sell an original copy of newspaper.
Firstly contact the newspaper direct. Most papers have an archive system and store old papers electronically. The Times newspaper is a popular choice for people to buy 'birthday' editions from. They have a section specifically set up for this so they are worth a try as well.