There is very little information available and it is often difficult to obtain. One of the main reasons being that the scientific research is virtually non existent. However, some work is presently being carried out in the US. Hopefully this will result in a wider comprehension of the syndrome and that it will be aknowledged as the actual disorder it is. The aim is to include the syndrome in the next edition of the DSM (Diagnostic and Statistical Manual of Mental Disorders). Maybe this can make help available in the future.
As for printed sources only one is readily available. It is the previously mentioned book "Apotemnophilia: information, questions, answers, and recommednations about self-demand amputation" by Gregg M. Furth, Ph. D. & Robert Smith, ChM, FRCSEd.
Other sources can be found on the Internet but please read with a critical eye.