I spent the evening on EBay, Oz, UK, and US, and nothing. Or nothing yet, anyway. Found another source in Holland, but much the same price.

It is possible that the battery is not finished, but was stored in a discharged condition, which means it will no longer accept a charge. Lithium-ion, you see.
They can apparently be revived, but no-one will tell me how, because often they explode in the process!
However, my son is doing a degree in electronics. Hhhhmm.