Good alternatives for peri peri include jalapenos, habanero and cayenne peppers. Or you could try ready made mixes of chili powder and paprika. You want to recreate the heat of piri piri without becoming overpowering and a mix of alternative peppers can be the right idea.
Cajun seasoning is made from salt, paprika, garlic, black and white pepper, onion powder, ground cumin, cayenne pepper and then oregano, thyme and any other suitable herbs you like to add. You can mix the paprika to use smoked, sweet or hot.