plumb center sell the bits, i know, as i helped some1 on the DIY forum link 2 IBC's
I showed them the whole tap from the ibs and they said they did not stock anything that would fit, is it on the diy site pics etc ?
no, it was done via PM's
from what i remmber it was a brass fitting into the IBC threaded hole and then a plastic barbed fitting off that
measure the size of the thread, at least you will have some idea on what you need