I think you may have to grit your teeth and go to a proper grown up shop!<br /><br />
Or perhaps you could find some "handkerchief lawn" somewhere and hem your own. I haven't seen any of that for years, but then I haven't actually looked!<br /><br />
Just a thought, as they won't actually be used as hankies, the fabric isn't all that important so long as it is good to embroider on and looks nice when it is finished.

Since you may be doing a lot of footwork to find a hankie to your liking I would also would suggest creating your own hankie. I also did this for both families in a wedding and used a decorative heart with the couples name and wedding date within. I then finished the edge with a lace for the females and a rope cording for the men and they looked really nice. Hope you are able to do the project to not only the brides liking but that you also will like the finished project even if it means doing another small project so they will get something that your heart was into creating for them. Good Luck

There is a lovely selection at Embroider This...if you could order and received in time...

I wouldn't shy away from making your own hanky. It may be your only choice. It probably takes more time to buy the fabric than it takes to stitch one up.

Try Google mens silk handkerchiefs might find something near you .
good luck