Out of print long ago, but you can still get secondhand copies from time to time. There's one available at the moment at a decent price: http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=148932008.

Frank Purslow's selections from the Hammond and Gardiner collections (also EFDSS and out of print, but we're still hoping for an eventual re-issue) have a good bit of Dorset material. You can also find them occasionally; most often the first, Marrow Bones. There are two listed just now:

http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=227077376

http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=219277778

These links will only work for a short while.