Cheap way to make one is 400 mm long piece of round hardwood, like an old shovel handle, drill holes at top and put 100 mm long 12mm round dowel in where it locks round frame and then file the bottom end of the 400 mm bit so its rounded on inside and screw and glue another bit of 400 mm round to make the base, slip some hose over the dowels to protect frame. I did this but threw it away and made em from steel, if i want to show a bike ever (if I even get one finished well enough) l'll smooth the welds and paint. My metal ones cost me nothing really, and are easy to clean up if i want to.
If you need i can send you a diagram with measurements.

That took ten minutes to make and isn't even cleaned up but would clean up easy.
cheers Tim