You need two axles for a standard four wheel wagon.
Small Quantity Of New & Sealed OO Gauge Wheel Set Parts-Bearings-Slaters-Gibson
Hornby OO Driving Wheel Set for Jinty/57XX/08 Locos Centre Wheel Drive
Triang-Hornby OO Driving Wheel Set for Jinty/57XX/08 Locos Front Wheel Drive
Hornby OO Gauge -Wheel Tender Wheel Motor .
Accurascale Class 55 Deltic EM Gauge Wheel Set, new unused spares