Mel - Baobeer and Jarakhus are not so commonly found. You get them in ayurvedic stores. Jarakhus is the root of the poppy seed plant.
Makhana - Are easily available in Indian stores. They are white puffy and look like popcorn and are pretty tasteless. They are lotus seeds that are popped just like corn kernels
Mitha Ittr - Also available in Indian stores. You can ask for Kewra essence. Kewra is a very aromatic flower that grows in the tropics. The essence of that flower is called Mitha Ittr
Out of all the ingredients in the list the only one that makes a difference to your palate is kewra. I normally add it to the biryani I make (it's like a Spanish version of Paella). It adds a depth of flavor that is very authentic in moghulai cuisine.
As far as the other ingredients go they are common to the Awadhi or Dum Pukht cuisine that was popular during the Moghul rule. It is not authentic to all Indian cuisine and I would bet that most palates are not that refined (even me being Indian) to differentiate the couple of these ingredients from others.
Makhana is normally used in sweet preparations.