Finding a nice road across the Alps shouldn't be a problem, go for the smaller roads, meaning less frequented mountain passes.
Travelling through Croatia, the most scenic route is along the coast to Dubrovnik, esp. the part south of Rijeka. Don't miss Trogir.
Montenegro has beauiful winding roads, since it is mostly very mountainous, but the coastal part past the town of Kotor isn't bad either.
Macedonia I don't know, but according to some ride reports also nice. Should you decide to pass through Albania,the main road going ftrom Shkodra via Tirana to the south is in good condition, but in the first parts fairly boring. The southern stretch around Gjirokaster is scenic. The coastal road in the south of Albania is brilliant, but in parts a bit rough for a street bike, since the last 100 kms before Sarande are under construction.
The last part up to the Greek border is very mountainous and good to ride. This is already part of the Pindos mountains, which reach far into Greece. Hence the northern parts of Greece are equally beautiful roads.
Only when we pause to wonder
do we go beyond the limits of our little lives.