CONTINUOUSWAVE

[Who is the] manufacturer of the latch for the swim platform [for a 1999 OUTRAGE 23] that goes over the ladder?

Are you referring to part identified as #49 on the diagram titled 230-Deck-Assembly-Parts-List-1999

Here: http://bostonwhaler.com.s3.amazonaws.com/resources/230-Outrage-Deck-Assembly-Sheet-1-of-2-1999.pdf

And listed as "Roller, catch" on the parts list

Here: http://bostonwhaler.com.s3.amazonaws.com/resources/230-Outrage-Deck-Assembly-Parts-List-1999.pdf

I would contact Sue Lodel, Parts Manager at Beacon/Twin Cities Marine, http://www.beacontcm.com or Nauset Marine's Parts desk, http://www.nausetmarine.com

I know this is a bit late. I had some broken hinges on my 1997 outrage. I used the parts diagram and found the part number. A dealer wanted $33 per hinge. I noticed a brand molded into the hinge and found the original manufacturer. I was able to use that info to buy 4 new hinges on ebay for less than $30 with shipping.
The hinges I had to replace were made by southco.