Already had a reply back from the companies Senior Product Manager.
"Thanks for the enquiry regarding wheel speed sensors for Toyota Supra mk4 models. As you noted there doesn’t appear to be a source in the aftermarket for these currently, but it is something we can look into having developed. Do you know the original Toyota part numbers you’re looking for? What is availability of samples like? They will be necessary if we need to develop from scratch."
I'll send him over the part numbers.
Does anyone have any old sensors to hand that could be given to the suppliers if need be? They would need to be intact including connector, clips, brackets etc.