This guy in Poland is selling air dams for a good price. I’ve not actually seen one, but he got good reviews. Below is a facebook link to his page. It has contact info.
BMW 3 E30 1983-1990 B6 / FRONT BUMPER SPOILER / PERFECT FIT | eBay?
Air dams
HiFiGuy
#2
@Ranger, Scott, do you think this would work with diving boards? I don’t have late bumpers, but I do need an air dam.
Ranger
#3
The guy’s ad says it will fit all model year E30s. Also, I looked over the pics closely and don’t see anything that would make the bits incompatible with early bumpers. Might have to do some imagineering, but that’s ok.
My suggestion would be to fasten it to car not too securely. My early air dam, for example, is supported by a little shelf I made under the AL bumper. The shelf carries the load. Then I’ve got 8 zip ties that hold it back so it can’t slide off the shelf. If the air dam takes a big hit, the zip ties break and the air dam slides off of the shelf and away from the car.
By not restraining the air dam too tightly, the air dam is more likely to remain intact if it gets torn off of the car. My last air dam lasted me 8yrs.