Pyaasa (the thirst) is a brilliant masterpiece. i've seen the movie thrice in four years and every time i watch it, it moulds itself to reveal new meanings and nuances...

Kagaz ke Phool (the paper flowers) is another Guru Dutt masterpiece. 

i don't know about outside india, but in india you can order Guru Dutt DVDs at thousands of shopes throughout the country. they can also be ordered through http://planetmonline.com  
and
http://www.easybuystore.com/filmindex.html

i don't think these sites ship outside india. guess your only hope is to get them if and when you or one of your friend travels to india.

a pity...