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You will find them under many different part numbers, made by many different manufacturers. Bosch started it long ago, and that's what they are referenced as, sort of like a adjustable wrench is called a "Crescent wrench". They are generally known as universal relays, and you will find them on the racks in the isles along with the circuit breakers, fuses, flashers, etc.
If you frequent the wrecking yards I almost wouldn't bother paying actual money for these at the store. They're ultra common on European cars, or Jeeps too, at least from the 1980s...With rare exception, though there are many different parts numbers, the differences are mostly superficial. Some have a little bracket attached, some don't. Some have a 'hood' that extends below the level of the contacts, some don't. Some even have four as opposed to five contact, which doesn't matter in most cases anyway since it's normally energized, then de-energized when the coil is energized (not used for most applications). The point is, they are all pretty much the same yet the cost of them in the parts stores can vary wildly. Just get used Bosch ones off any older VWs, Mercedes, etc...Probably better than the Chinese made ones you'll find in the stores now.
Regarding junkyards, inexplicably I don't seem to have a junkyard within striking distance of my home. Although many a front yard in my 'hood has a junker languishing within..