Langka (jackfruit) is easily found in public markets and even in the produce section of groceries. A friend who visited Tagaytay two weeks ago brought m some from the highlands along with three pieces of banana.
The thing with langka is that you have to eat it once you have opened the package so that you'll enjoy the sweetness and firmness of the fruit. Otherwise, you'll end up with soggy langka and you don't want that.
If you buy the whole jackfruit or the unshredded ones, you will get the seeds. Now, don't throw it away. You can still eat that and it tastes good, sorta like boiled highland legumes (remember Manny Pacquiao?). After getting all the seeds from this pack, I washed them thoroughly and cooked them with rice in my rice cooker. I got something to chew on while I was working. Healthier than roasted peanuts or chips! Saved me 6 pesos since I like snacking on Oishi's Patata when I work.