Not easy to find, and usually expensive when they do turn up!
This is how to make sure the RHD headlamps youve been offered are exactly that...
See the red area? That is the area of the lamp that creates the raised section of the beam on the left (to illuminate the kerbside) note that the same area at the other side of the light is flat... so light doesnt shine into oncoming traffics eyes.
So, on RHD lamps, the red section will be on the RIGHT side of the Vehicle. Thats Offside in the UK. Basically the section that angles down should be towards the middle of the road.
If thats not simple enough, the other method of identifying is the ARROW below the 'E Mark'.
The arrow will point to the LEFT of the vehicle (kerbside in the UK). Left Hand Drive lamps have NO ARROW.
Both headlamps on the vehicle should be the same.
The Red area is also the area you would mask when you drive on the continent. Usually you'd mask the area above to the line to make sure you dont dazzle at all.