They tend to be over here in the UK - people will put curry powder into their curries, without garam masala. Also, “curry powder” is the rough English translation my mother always used. Suffice it to say, the recipe calls for garam masala, as opposed to curry powder.
I’ve seen it, too. Some people even call garam masala “curry powder,” which isn’t really wrong, as curry powder is a fairly generic term which can describe many many different spice mixtures. You can substitute garam masala for curry powder, but it doesn’t work as well the other way round. (Although the main ingredients of these curry blends – coriander seeds and cumin – are present in both.) Garam masala is a fragrant blend (usually containing cinnamon and cardamom) which many curry powders have anyway.
I personally do not like most dry prepared Indian curry powders. They tend to be bland. Either toast and grind it yourself (time consuming, but worth it), or buy the paste in the jars. I echo don’t ask’s suggestion of Patak’s. They are very good and with them even the most novice cook can whip up a curry in no time.
BTW, Angua, Birmingham and Wolverhampton have the best Indian food I’ve ever tasted in my life (for good reason, too.) The only time I’ve ever had a vindaloo that kicked my ass was in the Midlands.
What I find works even better than garam masala, is to use dhana jeera, which is cumin and corriander seeds mixed in a specific proportion, and then to use whole cloves, cardamom, peppercorns, etc.