Hi John,
Not sure if you have already solved your search for your BM 6000 quad, but I thought you could try the following dealer in Denmark. I purchased my BM6000 from them and was very happy with the condition of the units, altho they are a little more expensive, you would be gaurenteed of a functioning unit.
http://www.radioogtveksperten.dk
They have one on their website list (they had it in stock when I purchased mine) but now it shows it as no stock .... but send an email to Soren there and they should be able to assist you.
Otherwise you could keep an eye on the following denmark sites, I saw one on dba.dk a while back.
www.lauritz.com, www.qxl.dk and www.dba.dk
Only downside is you would need to pay the shipping from denmark in each of these cases.
Well hope that this is of some assistance and you find the right piece to add to your growing collection.
Laurence.