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.
eplacements and alternatives. However remember that one of the beauties of garam masala is that it is ready made. So making up your own in bulk is useful as well! IN a pinch try some of these ideas.