Site says they are currently unavailable, but to clear things up:
The Ghost Overflow is available in 2 sizes as a DIY kit. It can be installed on any non-tempered glass aquarium or acrylic aquarium. Each Ghost Overflow includes a total of 5 bulkheads. The 24? Ghost Includes (2) 2? bulkheads for attaching it to the aquarium and (3) 1.5? bulkheads for plumbing. The 16? Ghost includes (2) 1.5? bulkheads for attaching it to the aquarium and (3) 1? bulkheads for plumbing. The 24? Ghost requires a 3? hole saw for installation. The 16? Ghost requires a 2 3/8? hole saw for installation. Hole saws are not included.