Just do a service request in the app. Do a parts only request in the "other" category. You can find the part number and description in the parts catalog.
epc.tesla.com
You can ask for parts cost of painted, unpainted, and labor costs for install. They will give you an itemized quote. Depending on how busy your SC is, it make take a couple of days for them to respond.
The "official" install may have more labor given it requires taking off the headlight and the front bumper. If you look on eBay, you can find other unofficial ways to replace the fender that does not require fully taking off the front bumper to take it the headlight, which can save some labor.
Note the service manual is free under service subscription:
service.tesla.com