You are right that all the 4x4 Duallies are XL. They only brought in one 4x4 F350 Dually, and it was the supercab XL with manual trans.

I personally would still buy one of those, as that way you get the compliance plate with a higher GVM and axle ratings, instead of doing the duallie (and manual trans) conversion and having to get engineers approval. I haven't been through this process myself, but those that I know who have still complain about it.
Then find a crashed XLT (or Lariat) in the US, and have the interior sent across (or just buy the bits you want off eBay). All the modules on these are plug and play, and they are before the complicated world of Can-Bus. This will also allow you to pick and choose the electronics, as to be honest a lot of the standard stuff on the XLT you won't want anyway (the "nicer stereo" for example will be a lot worse than a $100 unit from JB Hifi).

The only difficulty you might have would be airbags, but I am 99% certain they were fitted to XL's anyway.