Green tripe can be found from your local butcher ( by way of butcher, I'm referring to either goat/ lamb or cows/ buffalo in this country) on the fact that green tripe are those uncooked/ un bleached stomach.

Best timing to get large amount of green tripe at competitive rate?
Rahmadhan month/ before raya where local butcher will slaughter cows/ buffalo for sale.
Before Deepavali, that is for local goat tripe.
Whereas for venison tripe, it all depends on luck. I manage to get only once in the past 3 years, and that was before Hari Raya Haji, and it is relatively expensive compared to the goat/ cow's tripe, but worth every single cent.

Another tips for you, if you have a kampung to go back to, try getting from those butcher who also owns the animal or who bought from local farmers, best if the animals are kept kampung style ( grass fed in plantation + able to move around) rather than those raise and kept in feedlots.  Hope these helps.

Perut mentah or just describe it as perut hijau hijau tu.. 

Just got this from a pet shop, cant wait to try.

Heard it is one of the high grade dog food in Europe. Farmina Natural & Delicious