Does your installer mean he's having trouble finding the right CANPULSE adapter to install with the unit, or is he saying he can't find the right electronics bus in your car to plug into? Two different questions...
If he means the former, then tell him the Soundgate CANPULSE4 worked fine with an AVIC D3 in my 2008 Audi A4. According to one version of the 2008 Soundgate compatibility guide (attached for you), it should work for a 2006 Audi.
Below are some links to help...and I attached an old fit guide from Soundgate.
Better hurry...they are discontinuing the Soundgate product line (new company named "Kicker" says you can still buy existing stock at retailers, but is sorry they are no longer going to do the Soundgate stuff...).
http://www.sonicelectronix.com/item_11444_SoundGate+CANPULSE4+-Price+Good+Only+While+Supplies+Last-.html
http://www.kicker.com/soundgate
You may also need the correct harness for your vehicle (e.g., something like the CAN45PIO for Pioneer radios).
The new company "Kicker" has a fit guide on their website, but I think it's totally fouled up. Wouldn't trust it at all...
If, on the other hand, your installer means that he can't find the right wires/bus/harness to plug into that's a different question...there are definitely folks on here who can help, though.
Which does he mean?
Soundgate Application Guide 0302.pdf