I went to Vassilki on Lefkada Island in June 2018. Stayed 4 nights at Windclub - right on the beach

. Accommodation basic - but clean & well priced (booked via booking.com). Used the gear there - but it was average at best. There are plenty of other options for gear along the beach. We drove from Athens - easy drive - there is a small bridge across to Lefkada and Vassiliki is right at the bottom of the island. Hired a car at Athens Airport - Athens Car Rental - not one of the big guys - but would recommend. Check it out online.
Windsurfed 3 days - first 2 were good, the last was a bit hit & miss. I sailed on 6.something each day. Each afternoon there were several hundred people out on the water - looks busy from the beach, but when you're on the water there's plenty of room. Weather was really warm & was a good time to go. No wind in the morning - that leaves time to explore the island & keep wife happy.
There are plenty of places around Greece (or Croatia which we also visited) to windsurf - just do your research & fit it in with your plans - just be careful to not line up with the Euro holiday season as I suspect it could be manic & more expensive. June is before peak season.