In the six years or so since I first became acquainted with vintage AR speakers, I've had my eye out for replacement cloth that approximated the range of linens used on the grills.
I've never tried the 123 Stitch fabric, but I ordered several that I'd seen online brought up on forums or marketed as replacements. I haunted fabric and craft stores, looking at a galaxy of linens, burlaps, and cross-stitch fabrics.
I'm not as into vintage AR these days, but I like the aesthetic and planned to use similar linen on my next homebuilt pair of speakers.
And then, I hit the jackpot:
Curtains.
Looking through the curtains at JC Penny one day, I noticed that they had a couple that were dead ringers for vintage grill cloth - all of it made in China, all of it polyester.
It looks closer to the old linen than anything else I've tried, and at $25 per curtain, it's far and away the least expensive option I've examined.
Check it out!