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.

emm... in my kampung, green tripe and other parts of local beef/ mutton are normally sold in wet market. I'm not so sure about KL/ Selangor area, but I have seen green tripe sold in local pasar malam near my house on and off ( I stay in Bandar Kinrara Puchong), especially before or after Raya/ Raya Haji or on any occassion when our Muslim bro/ sis have celebrations and cows are slaughtered.

Usually I bought mine in bulk whenever I go back to kampung, both cow and goat tripe, price not much difference but I'm more comfortable buying in hometown 'cuz I know they're freshy slaughtered, grass fed and run free in oil palm plantation/ rubber estate.. You can try asking the butcher in your market/ pasar malam and see if they're able to keep the tripe for you rather than cooked + bleached one. I've also heard from other forumers that they have bought green tripe from NSK Kuchai Lama before too