Massaman curry paste is a mixture of different spices, lemongrass, peanuts, onions, and garlic - to name a few. Most of the ingredients are pretty common and easy to find, with the exception of lemongrass. If you can't find it, I think you could probably just leave it out and the recipe would still be delicious.
When I became a vegetarian, I had difficulty giving up two things - chicken fingers and burgers. I still miss chicken fingers, probably because they never really tasted like chicken to me, and I've never found a good vegetarian substitute, but burgers, I'm over. I'm now quite content sitting down to a veggie burger rather than a beef burger