Here's a little life hack:
Seek out a local screenprinter, especially one that does some work with costuming. They may not have experience printing flag silks, but explain to them the dimensions, the materials, and that you need a slot for a pole, and they would more than likely glad to do it for $20 to $30 a piece.
Googling "digital flag silks" will of course give you the big companies with ridiculous rates. Silkscreening on china silk isn't a big deal and if you pay more than $45 a piece, you're getting ripped off (assuming costs for artwork is not considered).