Yeah, KenW has the right idea, call LF. If I am not mistaken though...the LF wakesurfer uses their standard 2 bolt/screw pattern like their wakeboards, so I do believe that any LF wakeboarding fin would work.
Now, I also believe - but I would double check this before plunking down any cash - the HL boards use a single screw through the board and have two locating studs on either side of the female thread on the fin. If you remove those locating studs, then a HL fin will mate to a LF bolt pattern.
If so, then the HL 4.5" wakesurf fin should bolt up to your LF board in the center position. I know that fin is readily available online.