Re: Please recommend source to buy 1/72 scale Napoleonic paper flags
Warflags is the obvious place to go - a good range and free! Within the Warflags site there is a sub-section called 'Napflags' which is now 20 years old and has some good flags designed for '25mm' figures, which 20 years ago were actually 25mm as opposed to 28mm now.http://www.warflag.com/napflags/flaghtml/pr1808.htm
If you download these then you can scale on your computer screen to fit the true dimensions of a 1/72 flag.
Rofur flags are designed for 1/72 scale. They're out of business but you still can find them on EBay.
Co-incidentally, I just bought a lot of dozen or more sheets that included a bunch for the Prussian SYW-Napoleonic infantry units that I don't currently need but will keep for future projects.
As for Warflag - certainly. You can find divers flags from other sources by googling. A lot depends, I think, on the quality of your printer.
For some time, Ive been using an industrial quality laser printer from work that produces excellent flags. I use my own superior quality printer paper too.