Make Pepperoni out of Regular Salami
Pepperoni is basically just a spiced pork and beef salami with some smokiness in it, you could achieve a similar flavor by using some smoked chili powder like paprika or chipotle. You also aren't going to get very far trying to make a salami spicy by adding pepper to it beforehand, like injecting it with some sort of spice mix as there's not enough moisture to allow the spice to mix in. You'll have to add spice to the sliced salami, the question is how to apply that seasoning so the flavor seems to come from the salami when eating the pizza. Chili powders will burn in the high temperatures of a pizza oven, producing off flavors and an unappealing look, so sprinkling them on top of the salami slices is not the best idea. 

You have 2 good options:


Add the spice to the pizza sauce: this will make the whole pie taste of the spice and may not be what you want. It's the quickest and easiest solution though
Rub one side of each sliced salami piece with the spices, and then put them on the pizza spice side down. This will localize the spice around the salami slices, and put the salami between the spice powder and the heat source so it doesn't burn. This is a bit of extra work but I can't imagine it being that big a pain


Personally I'd go with option 2 as you'll get a nice hum of spice around the salami and some on it when you bite. It won't be quite a pepperoni but I bet it will be very close.