Why isn't the new LEGO CV joint available on Bricklink or Brickowl?
The sellers on bricklink/brickowl doesn't have ways to get elements before they become generally available.

As 42099 is brand new, pieces that are (currently) unique to that set probably hasn't made it to those sites yet. Have some patience, they will likely be there shortly.

Those sites rely on users submitting inventories so until somebody submits one, there won't be one (bricklink actually shows: "Inventory Pending Approval", so it probably won't be long).