Thanks for the mention robroy!
I have these available for £200 posted as mentioned above
I can also provide a gearbox building service so if you send your box down to me I can install them, with the option of shot peening and super-finishing the gearset for strength.
I stripped the teeth from 4th gear on my personal car from the input shaft using untreated gears for around 30k of abuse, so it’s something I recommend for customers making good power that like to abuse their box!