Yes, they are on our website in wheels section under accessories > wheel studs. They are $14.95 for a pack of 5. Let us know if there us anything else that we can help you with.
You are going to have better drive ability with a Twin Disc Clutch compared to a Single, but there really isn't a reason to use a Twin Disc at that amount of power. A Spec 3+ will handle that power just fine.
The price is the only "downside" to the twin discs, everything else is considered upside. Smooth engagement, longer life, easier pedal effort, holds more power etc. The main reason why the twins are a little more expansive, is because they include the flywheel. For example, a Spec stg 3+ is $499 on its own, then for a Spec Aluminum Flywheel it is $365, so right there your at $864. For about $150 more, you can get a Fidanza twin setup that will hold more power and probably offer better drivability. Let us know if you have any other questions.