where do I begin looking for a modeling agent

I wouldn't look for a modeling agent--instead you might want to talk to a few talent agents, the ones that book non-union background actors, some promotional models, etc.  The fact is that At 5'4" very few modeling agencies will consider you.

On the other hand, you're a lovely young woman who  is comfortable shooting nudes so you can probably do very well marketing yourself.  You might want to contact some of the non-agency models in your area and get their thoughts on how to proceed on that course.  If it were me, I'd start with  the 3rd list (https://www.modelmayhem.com/forums/post/927266) and The Big Buddy Thread (https://www.modelmayhem.com/forums/post/923164) to see if you can get some one-on-one help.

And, of course, keep up what you're doing with your casting notices and contacting photographers here on MM.   That's going to be a big part of your market.  And TF shoots can be your friend both in terms of building your portfolio and in terms of becoming known for when paying gigs come around.

All IMHO as always.