Where exactly is "here in Europe"?
Since many maintenance parts are shared between the 200, 700 and 900 series, they are easily available. There are many suppliers in the EU that will ship within Europe and/or EU or even worldwide, and Skandix in Germany is a well-known one. But there are more.

A single owner, who has cared for the car well, has the maintenance history on record AND when the body doesn't show signs of lots of rust is interesting to at least have a look at, regardless of the mileage.

306 k mi, or nearly 500,000 km as I would put it, is a high mileage, even for an old Volvo. But depending on how that distance was racked up, the engine may be in a reasonably good shape.
Where I live, most trips are short distance ones (< 10 km), and at that mileage the engine usually is well past its prime.
If where you live the trips are typically longer (say > 30 km), the engine may actually have less wear and tear than one would expect.

Or summarized: it depends...