No special access issues
Park as shown on the map. Take enough food and water and head out for about a 2km walk (First boulders around 1.8km from parking, last ones closer to 3km away). After the crossing of Route du liteau, you have reached the area. The area stretches on for a long way, so stay on Route du Milly until you reach your desired boulder. For the most eastern parts you can actually park on the east side. Both ways in are easy, but long.
There is also a third option, parking as for Isatis, and walking from there. From the parking of Franchard Isatis it's about 1.8km to reach Le Kraken, if you manage to navigate with the smaller paths taking you there. This approach will though take you over a hill, but might be as good of an option for some of the boulders.
As always, behave, leave no traces etc.