You can get replacement cables from J and R Trailer Repair
Home - JR REPAIR
or from Midget RV & Trailer Specialists
https://hilotrailerparts.webs.com/
I've read that some folks have found cable, cheaper, at various places, but you need special tools to 'make' the ends, etc. There's nothing special about the Hi-Lo cables, they're not spec'd just for Hi-Lo.
As for instructions, there are some detailed instructions on this forum. Make friends with the search function. It's not terrible easy, but with some digging around you can find it.
Good luck
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