I ordered the Sealand 711-M28 from Marine Sanitation and Supply in Seattle, Washington.
https://marinesan.com phone:877-607-8144
They have the option for the 3" center drain added for $25.
I paid $622.85 with $142.12 shipping to Kentucky, for a total of $764.97.
I would suggest calling them if you are interested, as they were very helpful in getting me the toilet I needed. They had white and bone coming in but were not sure if they had all been spoken for. A nice lady called me back and stated the white ones were spoken for but she had a bone colored one I could buy. Expensive option but I wanted to give another source in case they remain out of stock at Scamp.