I life you can buy everything with money, even painted corps napoleonics, incl flags.
Since i want to be the judge and painter of my own napoleonic battalions I produced always my own flags (fr austr bavarian westphal, ...) I only need a pdf or a goes picture of a polish flag that i can print out myself.
Paying +3 pound for one napoleonic flag is completely ideate and become even more if i would pay 6 time, +3 pound for my polish battalions.
I find it repelling that a common picture of an old flag, more than 200 years old, could not be given for free for those who want to create napoleonic war-games battalions !