O'Neill has been hit by several withdrawals for Friday's friendly in Adana, with Gareth McAuley, Chris Brunt, Michael O'Connor and Jamie Ward all pulling out of his initial 18-man squad.
Uncapped New York Red Bulls midfielder Jonny Steele was first called to bolster numbers, before left-back McGivern and centre-half McPake flew to Istanbul on Tuesday evening.
"It's a bit of a challenge with some of the withdrawals we've had but this is an opportunity for some of our players who are a bit untried at this level," said O'Neill.
"Credit to Ryan and to James, they jumped on a plane and arrived here late last night. That's the level of commitment we're looking for.
"They'll train but we have to be careful with them. It's a good opportunity for them to stake a claim on a permanent basis."
Shane Ferguson is another major doubt for the match after he was unable to fly out with the squad due to illness.
"Communications are ongoing but at the moment he is too ill to travel," added O'Neill.