There also a few larger scale (1/9) BMW and Zuendapp Bikes out there.
I think they were either by Heller, Italeri or Revell of Germany, not sure as they might have been repackaged kits.
Imai did a few Harleys in 1/12 scale,but they is gone now for a few years and their kits are scarce. Apart from that look at Gunze Sangyo High Tech kits, rare but some items are reissued at times.
Sorry, not much on any british bikes.