It's been a few years since I did a whole batch of these for various members here but I seem to recall that they were plug and play - just a single connection to the standard H4 plug on the car and then a little PCB on the light that kept the low beam on when highs were switched. If that is missing on yours then it needs to be replicated which isn't too hard to do - there are some HID harnesses that do the same thing.
All the light modules in those lights are standard Hella 90mm. Hella made a whole range in this size, from entry level right through to high performance xenon. The ones used in these lights are the low-mid-range models. The problem is that Hella updated the range a couple of years ago, going to LED, so getting replacements for what you have may be a little difficult and getting them at the right prices even harder. Currently prices range from around $100 for single focus halogen to over $1100 for bi-LED low/high beam. That's prices per module and you have 4 of them and doesn't include freight.
Narva also made some modules in this size, but very limited range. Also another low volume manufacturer that I can't recall the name of. The modules need to match the size, which is unusual, and also be fully self contained and waterproof so really there is nothing else that you can just 'drop in'.
IIRC, the part numbers are printed on the modules so start with those. There was only one significant Australian supplier who carried these and they were ridiculously expensive. A few places in the US had them and only some had the right hand drive, ECE spec ones that we need.
www.rallylights.com might be a good place to start.