Totally agree Wayne. In an ideal world finding a synthetic knot which feels and acts the same as a badger knot would be amazing but I've come to the realisation that will never happen so I stopped looking.You are going to struggle then Rob to be honest. The best thing you can do when changing from Badger to Synth is to not to try and compere Apples to Oranges. You'll never get the same feel of the SV from a Synth just like you wouldn't if you changed to a Boar.
they all have their own qualities, pro's and con's.
Bulbs are not a shape I've really come across in Synths, the knot closest to the SV are the AP Shave Co 2Bed and the Silksmoke but if you want backbone you'll have to set them low into the handle you choose. I suggest setting them with a well worked blob of Bluetack to test the feel, enough to test it on the face, you can then silicone it in.
Hope this helps?
I hadn't used a synth brush in ages (never have the urge to reach for the two I own).
However when I finally used the Simpsons T3 again the lather it created, along with the ease and speed it got me thinking about another synth brush. Hence this thread.