You can find Green Thai Curry Paste in ethnic shops and even in amazon, but nothing beats a freshly made curry paste. It keeps well and can be easily added to your favorite curries.
Grind the dry spices separately in a coffee grinder, immersion blender or mortar and pestle to make sure they are fine.
Then add the rest of the ingredients and blend until you have a thick and smooth paste.
If using a jug blender, you will need to add a little liquid to get it to blend, so if you're making green curry, if you are using the curry paste right away, you can add some of the coconut milk from the recipe.
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Notes
If you are making a big batch to freeze, a good, powerful food processor will work well. Also, I recommend using a powerful immersion blender which does a good job even for smaller amounts.