Curry powder isn't really traditionally Indian. My guess is it became popular to package "curry spice blends" for transport to the UK and beyond, so we're used to a "curry powder" concept. But the spices that make up the curry powders are used all the time, you just make up the spices when you cook.
I usually make a blend of the following for dal or chicken curries, but it really does vary every time:
Cumin/jeera (lots of it)
Fenugreek/methi (seeds, not leaves)
Red chili pepper
Black mustard seeds
Occasionally I'll add Kalonji/nigella seed or black cardamom (the latter in modest quantities).
I used to frequently buy the Madras brand curry powder, and if memory serves, one key component, at least to my nose, was fenugreek seed. But the easiest way is to hit up an Indian market and get nice big bags of all of the above (for what will be quite low prices) and then dedicate a coffee grinder as a spice mill. Then just make up a bit at a time whenever you need it.
Also "curry" is a term used all over the Middle East, South Asia, Southeast Asia, Africa, and the Caribbean that can denote any number of types of dishes, typically a well-spiced stew. It's a very generic term, so there's no standard curry.