I may have just what you're looking for. Came from my old TP20 that died electronically.You can have it complete with screwed spindle and pulley, end socket etc for the cost of postage.
The alloy bit measures 305mm from end to visible end.
PM me if you're interested. Photos may be possible.
Update: I've now separated the alloy tube from the other gubbins - and found the motor and the power lead with 6-pin plug.