I've been looking for an old handle that could fit a 28mm knot. I got this brush on eBay. When it arrived, I found the opening was only 26mm. But after some vigorous sanding, I was able to fit the knot. It is a 28mm Silvertip from TGN, and I can't wait to use it. I'll post a picture of the brush in bloom once I use it after the epoxy cures. Now I just need to find a handle for a 30mm knot.
Here's the brush prior to restoration.