You won't find many A&P mechanics that are current on it, but cable splicing
is covered in the FAA's AC 43.13 publication. The section is aimed at
repair of flying/bracing wires and control cables but the technique is the
same with heavier material.

A larger chandlery (sailboat parts shop) is likely your best bet to find
someone with actual experience.

I'm pleased to see the support for winch launching. Even in the wide-open
USA midwest they make sense (except maybe for wave entries).

Cheers,
Marc