RANS does indeed sell replacement foam and covers and the thinner combo foam/cover that I use on the captain's seat of our RANS Screamer.
Or, you can do what I did and get a new SlingMesh seat from RANS for your V-Rex. Warning: They cost too much. But worth it in the long run. Or, ride.
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Bacchetta Giro A20, RANS V-Rex, RANS Screamer