The distinctive thing about the R&B vest is its tailoring and the weight of the fabric. Most of the other vests I've seen are looser and drapier -- which I might actually prefer in many contexts, but if you're looking for a duplicate, it won't be quite the same.
So have you considered finding an old wool coat, maybe a vintage one from when they were more fitted, and getting the sleeves removed?
It depends on the weight you want, I suppose. I know one of my friends didn't buy the R&B vest because it was too warm for our climate and the outfits she had in mind.