Brimstone;
I thank you for your important question. I'll try my best to post what I know from an Islamic perspective.
Our Creator, God (Allah in Arabic) almighty says in the Holy Qur'an:
"He has only forbidden you dead meat, and blood, and the flesh of swine, and that on which any other name has been invoked besides that of ALLAH.
But if one is forced by necessity, without willful disobedience, nor transgressing due limits, then he is guiltless. For ALLAH is Oft-Forgiving, Most-Merciful."
[Holy Qur'an 2:173]
This verse shows that we are allowed to eat Haram food if we are in a state of extreme need.
Quote: However, what is classified as being unavailable?
I think (I am not a scholar) that the food is classified as being unavailable if:
1) That food does not exist in the place we live in
2) Or, we can't buy it
3) Or, we are in a situation similar to the one described in your second question (in a forest, in a desert...)
Quote: If you were stranded in a forest, with all the vegetation poisonous, and the only avaliable food wild pig, would you eat it? I have been given two conflicting answers from Muslim friends. One has said they would not be allowed to eat it while the other has said that in the Koran it is said that if only Harām food is avaliable for consumption, if it has to be eaten to stay alive, it must be.
If a person's life is threatened, he can eat forbidden food like wild pig, but only the necessary quantity to stay alive (remember in the above verse, God says:"without willful disobedience, nor transgressing due limits").
God (Allah) knows best.