I need to buy a MacBook Air screen

We are not Apple here, just other end users like you and do not have access to such information. Having said that, Apple does not sell spare parts. Take it to an authorized service provider or store and they will give you an estimate on replacing the screen.

https://www.gophermods.com/how-much-does-it-cost-to-replace-a-macbook-screen-at-the-apple-store/

$807.56 (US I assume) for this instance without any warranty protection

You might be better off in the long run just replacing the Mac..