how can i get my key barrel replaced without doing all doors? ?

hi i have an iveco daily van and my key wont turn, it was going stiff for the last few days,and after putting wd40 in it,it no longer will turn, i have now managed to lock steering too!!!!
do i have to see about replacing all the locks as that is what i have been told as selling them sepratley dosent seem to be an opption, any help would be greatley appreciated and sooner rather than later would be great. thanks peaple