The electrical plugs and housings are easy to find on ebay or at a bmw salvage yard, they came on various models throughout the 90's.
However it's not so easy to switch back and forth. I assume you have the sealed headlights, then the low beams are dual filament. Euro headlights use H1 single filament bulbs meaning your low's will turn off when you switch on the high's. To convert it correctly you have to modify the wiring at the fuse box to keep the low's on when you switch on the high's, for proper visibility.
It's a worthwhile upgrade if your willing to do the full conversion, maybe even add a HID kit. Otherwise I would do like deansweet said.