I am looking for a place to [camp][1] (tent, coming by bicycle or train), at walking distance from a beach, and not far from [Tokyo][2].

Any recommendation?

I have found a few lists of camping addresses, but no reasonably exhaustive map.  
There are lists in PDF format, but it is really hard to estimate location from that.  
The ideal would be a Google-Maps-based mashup showing all campings, if that exists?


  [1]: https://en.wikivoyage.org/wiki/Sleep#Camping
  [2]: https://en.wikivoyage.org/wiki/Tokyo