Not the cheapest ones, but great:
http://www.pingelonline.com/prodcat/fuel-valves.asp
http://www.pingelonline.com/motorcycle-fuel-valves/dual-outlet-3311-d-ch.asp
You may use a fuel tap with single outlet instead and a “T-shaped” connector between fuel tap and carbs.
Thread size at B-tanks is M22x1.
Cheers, Michael
