I believe the handlebars are from a BSA Bantam D1 and D3. They are still available new but the brazed on perches are a bit different on the new ones. MK0 on the right, MK1 on the left.

Both my MK1s and the MK0 have the same bars with English Doherty grips and twist throttle. I put a wider Aluminum bar on the Rust Bucket MK1 because I was riding it daily for awhile and the narrow BSA bars beat me up too much. I am trying to find a chrome plating shop. Eventually I want to get the Rust Bucket MK1 back to original.

More MK0/MK1 handlebar pics.

The kill switch is drilled and tapped on the left side of the MK0 bar and the same kill switch is clamped the right side of the MK1 bar.