Dester,
the reason no schools in South Africa will guarantee an Instructor position is that they like to have a choice in who instructs for them, and they tend to chose people who thye feel will fit into the environment, not just somebody who has paid for a rating, or even doen their whole training with them.
Most schools will consider employing an instructor after his/her training if they are competent and nice people.
Schools such as the US ones who offer a job before you have even started training do so as a means of making money, not out of the goodness of their hearts, nor for the benefit of the students who may end up with a pay-to-fly instructor who is more interested in the hobbs ticking over than the student gaining benefit.
I see you list your location as Iran, have you tried flying schools within the GCC? Your approach may be better appreciated there.
Good luck.