Try this http://uk.farnell.com/xp-power/iu1209sa/converter-dc-dc-2-1i-p-2w-9v/dp/1435417, will take 9V to 18V input and give you 9V out to go a barrel plug http://uk.farnell.com/multicomp/mp-136/plug-low-voltage-2-1mm/dp/1737256?MER=en-me-pd-r2-acce-con. You may find these on Ebay. 