Hi,
We too are in the Highlands (Nairn), have a 8 week old girl, and know exactly what you are going through!
We have just (finally) bought a Cali after 3 trips down south - one time-wasting one to Wales and two to the midlands - The highlands is a major headache from this perspective but then we have the long term advantage of staying here so can enjoy empty roads and fantastic scenery / wild camping sites less than 10 mins. from home! ( I know which I'd choose!!)
We ultimately bought from a VW dealer but after long discussions and lots of pictures all the vans we looked at were "held" for us pending viewing so we had first refusal - avoiding the risk of travelling hundreds of miles only to find the van sold!. You have to move fast for the good ones (particularly at this time of year)
We hired a converted VW van for one of the trips (baby and all!) a return trip to Coventry - made a long weekend of it - costly to hire but less stressful than a mad blast in the car with an unhappy baby. This also provided a final confirmation that a camper / cali was the way we wanted to go - it's a big investment and although they hold their value well you don't want to be buying to use a few times only and then sell again in the winter.
You may find someone from south who would be willing to bring their van north for a Demo but I for one would be reluctant to travel a long way for a potential sale without some form of commitment from the buyer or at least an agreement to contribute to fuel costs or similar if the sale didn't work out. You might get lucky and find someone who wants a tour of the highlands before selling - you could meet them buy the van for a lump sum and some one way rail tickets...
I think that VW dealers have the ability to access nationwide transport at (fairly) reasonable cost,particularly if you're willing to wait for a bit. In that way you buy take a trip to view and commit then have the van delivered without lots of time and long motorway miles.
If you're spending Cali money on a "van" then I'd expect you could argue for free delivery to Hawco's or similar.
What sort of van are you looking for? Happy to discuss any further thoughts you have. I need to pcik some stuff up from the south coast so if you see a van down there you like you can collect my stuff for me!!
Kind regards
Warwick