automatic p.o

hi

we want to automate procedure from mrp to p.o mean

when mrp runs it creates p.req my company has contract with different vendors so they want system should use those vendors as source of supply automaticlly and then ceate p,o

i know if we have info records and source of supply and quota system does it for you but here i want system to pick vendor i have contract with(contract and schedualing agreement)

any help is much appriciated

thanks