leave for preparing civil services exam

Hi...I am working in PSU bank and right now under probation. I want to appear in upcoming civil services examination. For that I need leave from my organisation. But as per my knowledge there is no such provision for exam preparation leave. I tried to prepare for the same while working but I found that I need sufficient time for preparation which I am not getting right now. Pl suggest me what is the alternative to avail leave. I am also ready for leave without pay. Pl guide me.