A few random thoughts:
The obvious route is a direct flight over the Alps to somewhere in Croatia. Losinj LDLO is a nice little island with a fully international airport (a wooden hut) and 60p/litre avgas.
From there you could do Turkey (the near bit) in one more leg.
The Belgium - Germany - Austria route crosses the Alps at a lower level than the route from Switzerland, but a portable oxygen kit is still desirable for VMC on top.
Not much avgas in Greece. Corfu LGKR has avgas, then Mykonos LGMK. Corfu would thus make a good final stop on the way to Turkey.
Alternatively Sitia LGST has avgas and is also a port of entry, at times of the year anyway.
Once over the Alps, the weather tends to be a lot better, which is why crossing the Alps in one leg from the UK is a good idea. Far better to be sitting here at home waiting for wx to improve than doing the same in a £200/night hotel in Switzerland eating £20 Swiss sandwiches.
Another way is to fly down to Dubrovnik LDDU, avgas is there, and fly direct to Turkey from there. This may be tricky - Montenegro, Albania and Macedonia are not entirely casual about routings and I recall having some fun there when I used to go VFR.
Last I heard, N-reg planes are 24hr PPR in Turkey.
The plane will need transfer to a Turkish reg if it is to be used for training, and they really ought to get their ducks in a row for this before buying one!
It will be a great trip - bring a camera!
You will need VFR charts and past the end of Italy there are just the very old U.S. ONC/TPC charts which show out of date airspace etc.
I've sent you an email with some more details.