Your best bet for the Ouachita River is the Forsythe Park Boat launch in Monroe. Also the Lazarre Pointe Launch in West Monroe is good. If you want to fish further north than Monroe, try Moon Lake Marina or Alabama Landing (way north towards Felsenthal. South of Monroe towards Columbia, LA you can use Riverton Boat Launch. I grew up fishing the Ouachita and really miss it. It's a beautiful river. Good luck.
RRWC launches found at: http://www.redriverwaterway.com/rec_areas.aspx
Prestnly, they have closed all launches, though I wonder if they can close the private launches, like in the Searcy oxbow south of Pineville, and the one north of Colfax?
http://lamarinas.losco.lsu.edu/