They are also called "tone generator/induction amplifier kits". You can buy them at any electronics related store, as well as most hardware stores (home depot, lowes, menards, etc.). They are used for tracing telephone, cable TV, network wires, etc.
As for splicing with the least resistance, I'd say actually soldering them and using waterproof heat shrink wrapping would give you the best connection. But, that's a lot of work and you need a cordless soldering iron.