Question

Is there a specific place/location in Pokemon platinum to get the Lucky egg??

Answer 1

Wild Chansey have a 5% chance to be holding one. However, I don't think you can get one in any other way in Platinum.

Answer 2

Im afraid not. Lucky Eggs are held by wild Chansey in which you have 5% of finding them. To make it easier to find, you can get a Pokemon with the ability Frisk and that way every time you encounter a Chansey it will tell you if it has or not a Lucky Egg. Also Pokemon with Compound Eyes attract Pokemon with held items (in this case you would want a Chansey with a Lucky Egg)

Hope this Helps