How can I get the replacement parts...

Olly Fair, this is the repair forum. Although there may be a few repair technicians on here, I suspect you'll have better luck speaking with the iFixit Store personnel about obtaining genuine Apple and Google phone parts. You can contact them at support@ifixit.com.

Good afternoon from Australia,

Unfortunately there are no parts that are genuine from apple unless you are based in the united states, where they are basically as expensive as sending it into Apple. This is extremely unfortunate as repair businesses like yours can't find proper parts. My advice (As someone who doesn't run a repair shop but has a little know-how) is to find the reviews section of a page and check if people have been scammed as it's a generally reliable place. Alternatively, buy some cheap parts phones and salvage those as another option as those are genuine Apple parts. iCloud locked phones are generally a great place to start.