Nearly forty quid for a plastic gear? I did say it was a money spinner for them!
You are prolly in the unfortunate position of not having an operational mill to make one (or more) so very easily.
With a mill and rotary table (preferably with dividing plates) – a simple task of cutting the teeth, onto a blank, using an approx £20 cutter (or even a home ground flycutter?). Keyway could be broached, cut on a mill or lathe or drilled and filed to shape manually.
Can be done on a lathe quite effectively with a milling slide.
Loads of u-toob vids on the subject. Xynudu is one of many practical u-toobers with examples on-line.
If you have a comprehensive dro, one can easily make an indexing plate on a mill. A spin indexer may suffice, as an alternative to a rotary table, dependent on the number of teeth to be cut.
If you know the dimensions and mod number etc, HPC gears (or others) could probably supply.
I quite like gear cutting, although infuriating if something goes wrong near the end. BTDT!
Like most things, once you have done one, it is easy to knock out new gears.