Thanks for comments, gentlemen.
The flags were home made. There's a Swedish website on the GNW which had flags of most (or all) of the regiments at battles. And flags for Sweden, Russian and Saxony. I'll try to find the link later today if I still have it. I think I may also have used Russian website.
The flags may only have displayed one side. I can't remember now which flags showed both obverse and reverse.
Anyway. I copied the flags as a jpeg picture, then did some work in MS Paint to mirror image the single side and turn it into a two sided, obverse and reverse. I had to remember to allow enough space between the two sides for the flag to wrap around the standard pole.
Then I did some work to import all the flags I'd made into a MS Word doc. I then printed out some test sheets and re-sized the flags to get a size that looked good on the model. Or looked good to me.

I ended up with infantry flags about 22mm high and, if I remember, the cavalry flags were about 14 or 16mm high.
It was a long process but I was happy with the end result.
Also, as a wee postscript. Blue Moon standard bearers have cast-on flag poles and they are quite thick with a tendency to bend and maybe break just above the hand. It's a nuisance, and if I was to do them all again, I would remove the flag pole and replace it with wire. I used a unbent paperclip.
And strangely, the Blue Moon pikemen come with closed hands and no pike, so the hands have to be drilled to take a wire (or paperclip) pike.
I hope all this helps,
cheers,
Tom