Where can you find the pamtre berrie in diamond?

you can get it in amity square. here's an easy way:

step1: get a cute Pokemon.

step2:optional get the poketch app footstep counter(counts the number of steps you've taken) the footstep counter is in jubilife city. talk to the boss inside the company. you must have a gym badge first or something like that...

step3: go into amity square in hearthome city

step4: do this step only if you have the app. once you are in amity square, press the C button on your app on your touch screen.

step5: you should use the app for this. start walking around and once your app number hits 200, tap your control pad slightly so you're facing your Pokemon press Abutton.

NOTE: this may take a while because a pamtre berry is rare but with the poketch steps counter app, it does save you time. hope i helped!!! ^-^.