Your a braver Man than me!
Anyone who wants a 6 month supply has TRUELY never eaten them in a real live situation long enough to get past the fun stage to get to the fact that those things suck!
I ate MRE's in IRAQ for 2 meals a day for over 6 month strait at a forward operating base in IRAQ. You want a 6 months supply your very brave.
In any case look up army surplus stores in your area usually around an army base! Usually there is soldiers comming in pawning stuff(NOT THAT THEY CAN LEGALLY PAWN THEM) but they usually have some. I think the last time i went into the army surplus near Ft. Lenordwoood when i was down there for training i am pretty sure they had some.
Just do a search on internet for for army surplus stores and give em a call. and they should tell you what they got!
I am not sure what they are second hand but, as i recall they were over a hundred bucks a case so 6 months supply is serioiusly a chunk of money!
My 2 cents