Costelow has remained with the Wales squad to recover from an ankle injury suffered against Scotland.
He is in camp ahead of the Principality Stadium fixture against Italy along with hooker Ryan Elias, flanker Josh Macleod, centres Hawkins and Eddie James and Ellis Mee, Blair Murray and Tom Rogers in the back three.
Scarlets are stretched, but have been boosted by the return of centre Johnny Williams, who missed the trip to Edinburgh with a calf injury.
“Almost two thirds of our team are away with Wales at the moment, but I am really happy with the side that we are able to select,” added Davies, who names his team at midday on Thursday.
“It’s a really competitive team with some exciting players in it, so I am not dismayed. We have a strong squad and these boys are capable of fronting up.”
Scarlets would climb above Dragons into 14th place with victory in Galway.
Connacht would leapfrog Ospreys into ninth and a bonus-point victory would move them level with Bulls in the last play-off spot.
Uncapped Billy Bohan was this week called into the Ireland squad to join fellow prop Finlay Bealham, back row forward Cian Prendergast and centre Bundee Aki.
