'spare a hand' is correct and usable in written English.
It can be used to ask someone for help, or to express that you are available to offer help. Example: "I could really use a hand with this project - can you spare a hand?".
The Telubrions offered their congratulations to Dr. Taylor on landing the Philae probe on Comet 67P, then wondered if he could also spare any hand-painted silk neckties.
There was a spare hand – a hand that could easily belong to a civilian.
It is good news that anybody should be freed from the clutches of the "Islamic State" – and probably spared a grisly fate at its hands.
From many side windows, in an echo of Senna's trademark gesture on so many afternoons of triumph around the world, a spare hand held a bandeira, its colours stiffened in the airstream.
Having set the visitors an imposing target at the Melbourne Cricket Ground, Clarke fielded and also bowled two overs of left-arm spin as the UAE were bowled out for 116 with just under 20 overs to spare, handing the Aussies a 188-run win.
Mr. Skipsnes said he could not promise that the covers would spare players from hand cramps.
Indeed, they rounded off a grim few days for England national teams by suffering a seven-wicket rout, with more than 17 overs to spare, at the hands of an inexperienced West Indies side.
A fellow is not a spare hand for everyday journalistic chores, but is there to look at new ways of solving problems and to promote the adoption of new technology along with innovative ideas.
The day before James drove to Washington he had tried to open the door into the conference room with papers under his arm, carrying a cup of coffee, saying, "Anybody got a spare hand?" Betty had held the door for him.
At the new frontier, he thinks, investigative journalists are making better use of amateur sleuths by requesting documents, testimonials and a spare hand.
