how to get a citroen relay rear bulb holder ?

i have a citroen relay 07 plate which i had a cracked rear near side brake lens on , i bought a replacement but as most it came without a bulb holder , which some of the terminals had gone slightly rusty making all the van lights go crazy .
i removed and cleaned it all and all is well apart from the near side brake light doesnt work , but lights do , i have changed all bulbs with no joy ,any ideas , cheers jamie