Kookie: As far as I know, there is no "stock" Oday 23 trailer; lots of different manufacturers, with different designs will accomodate the 23. You can have a new one made for you by loadmaster or ezload (or any of a dozen other companies), or you can look for a used one. However, the last time I looked (about 10 years ago), the cost of a new trailer was about as much as I had paid for my boat; used ones in good condition were not that much less.
If you are only looking to move your boat for the one time, you might want to consider having it professionally trucked. It's probably cheaper.
Your follow up: the I, P, E, and J measurements are related to the sail plan, and are not germaine to finding the right trailer.