Which country's notes do you want? The Fed and Note Printing Australia both do uncut sheets, and I wouldn't be surprised if the Singapore Mint (do they handle notes as well as coins?) do them as well.
No need to PM random shady people; let me know which country you're after and I'll post it here.
US dollars: the Bureau of Engraving and Printing sells uncut sheets through their cleverly named
Money Factory online store, right here.
Aussie dollars: Note Printing Australia doesn't sell banknotes directly, but if you get in touch with the good folks at
Downies they might be able to hook you up with some uncut sheets.