As Ed has said it is quite easy to find the paste, even in supermarkets, certainly easier than trying to lay your hands on some of the ingredients.
I've made this one and made it more filling by adding a handful of noodles.
16 raw shell-on king prawns
Dash of oil
4 lime leaves, roughly torn
2 lemongrass stalks, cut into 5cm pieces and crushed
2 slices galangal (optional)
2 bird's eyes chillies, finely sliced
1 tbsp palm sugar
Juice of 1½ limes
2 tbsp fish sauce
Handful of coriander or Thai basil leaves, torn, to serve
1. Shell the prawns and set the meat aside. Heat the oil in a pan on a medium-high flame, and fry the shells until pink. Add 1 litre of water and bring to a simmer, then strain and discard the shells.
2. Return the prawn stock to a clean pan, and add the lime leaves, lemongrass and galangal. Bring to a simmer and leave to infuse for 5 minutes, then add the chillies and simmer for another couple of minutes.
3. Add the prawns and cook through until pink, then take off the heat and stir in the sugar, lime juice and fish sauce. Taste for seasoning, and then pour into bowls. Garnish with coriander or basil and serve immediately.