Most airline pilots have long ago let their SEA & instructor ratings lapse.
Airlines are reluctant to let their instructional staff go so the trainers mostly get protected by this when the job cuts come.
A large chunk of the airline pilot population are not very good pilots when it comes to hand flying aircraft, years of de-skilling by over reliance on autoflight have taken there toll. So all in all you are not likely to find many ex-airline pilots that you would wish to be your instructor.
There are exceptions to this rule and they are likely to come from the charter airlines who spent summers flying visual approaches into small Greek islands