Hello Kappa. Is this related to your previous question on iCloud locked devices? As I mentioned, there are several main components that are "keyed" together. That means somewhere inside, they share a similar key, or serial number if you will. There are ways to program the NAND and EEPROM but not the CPU.
What that means is that you can't just buy a CPU or a BaseBand IC and expect to change it on another device. You have to replace all of them (CPU/NAND/BB/EEPROM and Home Button) at the same time and they all have to come from the same, non-iCloud locked device. This is not like replacing a Tristar or MESON IC.
Some places do sell sets based on the device you are trying to unlock; you're best bet is to look at Aliexpress. However, I don't see the point when you could just buy the working logic board instead.