B40 WD Engine sprocket

[Denaro]

I'm looking at ways to improve the gearing on my B40 WD which feels like it has three 1st gears and a top gear good for about 40mph max.

An old thread "B40 WD gear ratio" suggested replacing the standard 23T engine sprocket with a 28T sprocket from a B44 Victor.
Sadly I can't find any 28T sprockets anywhere. Does anyone know where to find one or any other suggestions to make the bike more usable?

Thanks