Today I've joined the Guernésiais Facebook page. It hasn't been very active and there aren't many members. Like me, those who have posted have an interest in learning the language, but are having trouble finding resources. In my post I mentioned the BBC Archive of Guernsey French lessons with the voice recordings and the Grammatical Survey by De Garis, and I asked if anyone knew of any other available resources.
Over a month ago, I asked a librarian at my university to help me locate Marie De Garis' Dictiounnaire Angllais-Guernésiais . There is one on reserve at another campus (a 5 hour drive from here), but the librarian said she would check with other universities in Canada and the US, if need be, to see if there was a copy available to loan. This dictionary is quite rare and the latest edition was published in 1982, so I haven't been holding my breath...I should go in and check on the status anyways though.
While trying to find a photo of the the Dictiounnaire Angllais-Guernesiais, I came across a much older Dictionnaire franco-normand (1870) by Georges Métivier. The book is available online from google books and after reading the first few pages I found that Métivier has focused on the Guernsey dialect! The word collection, as he calls it, is written in French, and he makes linguistic observations and links many words to Celtic, Teutonic (Germanic), and Roman origins.