Can i have a leather cheek pad on my iron sight BPCR rifle ? The rules under scope BPCR address this issue..but i can't find anything under irons.

Yes you can. HOWEVER, it is subject to being at least 3/4" below the midline of the bore, as is the comb. In other words, if you have a stock comb that is right on the line of legality, you could not add a cheek piece to it.

These guys make good ones however tall you want them, and they are quick too http://www.cheeknstock.com/