Underdrive alternator pulley?

Where can I get one of these?

My mates car keeps popping alternators and I have a feeling it’s purely from over spinning the unit.
We only run are cars on the track so the engine spends most of it’s life between 6-8K rpm.
I have a new OEM unit but I have sourced a Denso model for my mates car (cheaper here in the states and a better unit overall). I know it’s only a matter of time before mine goes tits up

Try Power Master Motorsports - power pulleys

they have a good section explaining the theory as well.