Schools class front bogie retention

[ColinB]

My Schools class loco R 3194 has lost the piece of plastic that holds the front bogie on, it goes behind the bogie retaining plate to hold it on. Looking on one of my other Schools Class Locos it looks like a piece of PVC tubing pushed onto it. Any idea what it is, so I can make a replace. Front bogies for this loco have for a long time been unobtainable, so I need to fix it.