In modern phones the key part numbers for ICs aren't going to correspond to anything you can buy.
At best, you can see the part numbers for the passives and their alternate suppliers. The part numbers for most of the actives aren't going to be useful to anyone outside of the manufacturing chain for these parts. A repair tech would simply source the donor parts from an identical phone model.
...on the open market.
However, if your repair shop exists just down the street from one of Apple's component supplier's factories, then knowing the part number of one of the ICs or other actives, might be enough to let you walk in there one day and submit a hand-written PO for a few boxes of said part (...as a cash transaction, of course.)
Laptops, motherboards, microwave ovens and whatever else has "commodity PCBs" are much more repairable than the highly size-optimized phone market.
My mom's Samsung phone suddenly failed to charge a year ago, but in a weird way. Tried some tricks but it ended up getting stuck on a black screen during boot.
I handed it to a repair shop in town that had good reviews. Three days later they called back. I asked what was wrong, and it turned out they had to replace one charging chip, a power sequencing chip and a third chip I can't recall the purpose of, along with the USB port. The reason it took so long was they got a bit further for each chip they swapped.
I'm in Norway where prices are high, and we have a 25% VAT on top. I paid $180 including VAT, or $144 before VAT.
For that I might have gotten a very cheap Android phone on sale, however my mom's phone was a premium model from a few years earlier. Besides, less e-waste and saved me time reinstalling everything. Personally I think the repair was well worth it.
There's discussion here in Norway to drop VAT on repair jobs such as this, and in that case I think it would definitely make sense to repair such cases.