I was doing research on this based on your PM, Montreal, when you posted...
Ok, I assume you are after a lamp with a sidelight(parking light) built in to satisfy the MOT test requirement of seperating the amber direction indicator lamps from the parking lamps?
The headlamps system on the Airstream looks the same as on the 1987 Suburban body... 2 stacked 165mm 4" x 6" sealed beams...
Here is what I found out...
Part numbers...
Low beam H4656 quotes it being the same as a 1980-1985 Audi.
High Beam H4651 also quoted at same part number as 1980 -1985 Audi
Some searches turned up this H4 conversion... I bet a similar one is available in the UK...
Note it has a plastic body... you could drill a small hole and add a 5w bulb if that would be legal..
H4651 Sealed Beam Conversion Headlight
Painless Wiring do a relay kit to make all 4 lamps come on at once...
Could not find it for sure, but here is a similar one...
http://www.brightheadlights-hid.com/...-harnesses.htm