There's heaps of different undersuits available.
I used a Receka one last year, it wasn't the race one but it didn't survive a crash at Cadwell at the start of the year.
I replaced it with an EDZ suit which I'm yet to ride in but trying them on with the leathers is good. I also like the idea of the Kushitani undersuits - I'm going to try one of those soon hopefully.
HTH