You can not get PP ups in Pokemon platinum.
Nowhere. However, there are feathers that you can find on the Driftveil Drawbridge, which mimic pp ups, hp ups, zinc, carbos, etc.
The Energy Guru at the outdoor market in Slateport city sells carbos, zinc, iron,etc. but he does not sell PP ups or HP ups. Basically, you cannot buy PP ups or HP ups
pp ups are things that put you're Pokemon's pp up
You can buy pp ups at the Shopping Mall 9 on Route 9.
you find pp ups throughout your adventure
if you fly to nimbassa or walk the trash can closest to a vending machine in front of the pokemon center has one inside it.
Blizzard normally has 5 PP, which can go up to a maximum of 8 PP using PP Ups.
Yes. There a little tricky to find
You cannot buy PP Ups or Elixirs/Ethers in Pokemon Platinum. You can find them around the map, however.
You can win them in the lottery in Juniville city.
You need to find them or buy them at Veilstone City.