The phrase "a spare set of" is correct and usable in written English.
It can be used when referring to an additional or backup collection of items, typically used when the primary set is unavailable or needs replacement.
Example: "I always keep a spare set of keys in case I lock myself out of the house."
Alternatives: "an extra set of" or "a backup set of".
"You can't just pull out a spare set of lungs from your back pocket.
If there's time, it might be possible to source a spare set of shirts outside the ground.
He has given the narrator a spare set of keys, and now wants the narrator to wait for him to let him in.
The alarm bells started ringing when he got a call from the RAC asking if he had a spare set of keys – which he did not.
Before leaving the trailhead, hide a spare set of keys somewhere on the vehicle and tell your partner where they are.
Hamilton finished two tenths of a second quicker than Rosberg in Q1, in which both drivers managed to save a spare set of the quicker soft tyres for the race, and three tenths in Q2.
"Le Temps, L'Horloge" ("Time and the Watch") is a spare setting of three poems by Jean Tardieu, as economical in texture as it is in length.
With Sunday's Bears-Packers clash looming like some atavistic rite, it is also a good moment to recall that in ancient times, sports writers and broadcasters not only had easier access to athletes, but also operated under a comparatively spare set of rules.
In my own time, I've lost mobile phones, wallets, keys, my glasses, an entire spare set of clothes, endless pairs of tweezers, umbrellas, a striking embellished cardigan and a splendid peacock chair.
With a spare set, stark lighting and an ensemble of superb dancers, "Gardel" — which is performed in Spanish but features an audio translation — is a descendant of "Cabaret," "Chicago" and other musicals that inject a jazzy, soulful spirit into smiling musical theater.
With us came one spare set of kit, a few clothes for the evening, wash bags and wet weather gear, all crammed into the smallest possible saddle bags, along with puncture repair kits and emergency supplies of water and chocolate.
