Is it permissible to work in non-Islamic banks in non-Muslim countries when there is no Islamic bank available and it is difficult to find other employment?

Your inability to find a permissible job except in usurious banks does not make it lawful for you to commit what is forbidden and cooperate with those involved in it, for Allah the Almighty says: "And do not cooperate in sin and aggression." You can search for work in Islamic countries, for whoever fears Allah, He will provide for him from where he does not expect, and whoever gives up something for the sake of Allah, Allah will compensate him with something better.