I will be traveling to Monvemvasia, Greece from Athens to attend a wedding in June of 2019 is there any car service who would drive me from Athens to Monvemvasia and do some exploring along the way?
I’m sure there are, but it would be expensive. I was recently chatting to a driver for Welcome Pickups who does a day tour of the Peloponnese for 300 euros. It was very flexible and I imagine they would do something for you, but the price would include them getting back to Athens so would be more than the day tour.
Their site is here
There are probably other companies who would do the same.
Welcome pickups is probably the best known private transfer service. We have used Athens city cab which is very reliable. They offer transfer service but also a new service where they pick you up and drive your rental car to your destination so you will have use of it when you need it.