I had this exact same problem with my Danish Modern. I looked in all kinds of fabric stores. I never found anything close. I ended up getting a piece from Richmond Design. I looked for the fabric on his E-Bay store , but he must be out. Check back regularly, as he seems to get different cloths all the time. That is if you don't mind waiting a bit.
The the grille cloth suppler that made lots for the antique radio community went bankrupt several years back. So patterns that were in high demand are no longer available.
Tony
https://www.ebay.com/str/richmonddesignsinc