Raritan wasn't lame; YOU have to tell them which size it is. Crown Heads, in the last 42 years, have come in a number of different versions. They don't use only one size toilet bowl and toilet seat. It's up to you to tell them which one it is - the people there are not psychic - at least not yet!
Lift up the seat and look at the top opening of the toilet bowl. If it is perfectly round, it takes a Standard marine size seat (Raritan part # 1238A). This is notably smaller than your toilet seat at home, and is not interchangeable with a household size toilet seat.
If the opening at the top of the bowl is oval-shaped, longer from front to rear than from side to side, it uses a Hi-Boy or household-size seat (Raritan part # 1245). This is the same size as a standard round-front household toilet seat. Those are the two sizes that have been used on a Crown Head through the years. No Crown Head uses the newer elongated type toilet seat, where the front comes more or less to a point - although Raritan's "Alantes Freedom" series is available with an elongated bowl and seat.
Standard marine size = much smaller than at home
Household Size (also sometimes called Hi-Boy) = standard household (round front) size.
The household size can be purchased at any Home Depot, Wal-Mart or Lowe's. The standard marine size cannot. You must get it at a marine store, directly from the toilet manufacturer, from BoatFix, or from some RV dealerships.