Individual keyboard parts are not available from Dell - the keyboard will need to be replaced.

The service manual has the details:

https://www.dell.com/support/manuals/en-us/alienware-m15-r5-laptop/alienware-m15-ryzen-edition-r5-setup-specs/keyboard?guid=guid-f4d96b7c-8a4a-4f24-8b88-1f81d17905bb&lang=en-us

It appears the keyboard-palmrest assembly is a single part that needs to be replaced as such.

https://www.ebay.com/itm/385126063418?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=385126063418&targetid=1530439035971&device=c&mktype=pla&googleloc=9003434&poi=&campaignid=19851828444&mkgroupid=145880009014&rlsatarget=pla-1530439035971&abcId=9307249&merchantid=633255108&gclid=Cj0KCQjwy9-kBhCHARIsAHpBjHi0lCKBE2JCsfY7k8B2v5eR0PcUoJ-yTJXxrgURCZqIu8oi5wrmcaoaAhHEEALw_wcB