First off all there are 2 cables for the BG8000.
There is the power cord and there is the DIN wire which can have either 5 or 7 pins in both ends. Fully used in an Beolab 8000 system(or just a Beomaster 8000/6000) the 7 pin is for data link. You will need a DIN/RCA cable. Tjeck Lazerware on Ebay.
What parts do you need? As your BG seems to be very good you properly don't need much. As it's early '80s parts are for the most part difficult and the worst thing is the tacho disc unless yours have a one of metal. Some BG8000 has the metal type from the factory allready installed. Otherwise the celluid disc will vanish over time.
Now the good news is the Beoworld member Dillen has made metal tacho discs and it's the only place you can get one. B&O does not make spareparts for Beograms and neither do anyone else for that matter exept Soundsmith for the cartridges.
He can help you with any problem that might come up and also has capistor kits specially made.
The original cartridge is the MMC20CL and you got 2 ways to get one.Either a used/NOS one or go to Soundsmith to pick one. Soundsmith make great cartridges but a bit expensive and the others is a hit and miss. The age make the suspension go to pieces.
I got a Soundsmith for my BG8002 and the BG itself has cost alot to get fixed but I like the sound and everything so yes it's worth it. As long as you can get it repaired and with Beoworld you can.