Where to get a "swivel" from???

[fyrbuilder]

I have noticed on a number of crane builds that the hydraulics and electrical are running up the booms to power the cylinders and lights. I know on full scale aerial trucks they use a "swivel" under the aerial that the hydraulics and electrical go through so that the aerial can continuously turn without damaging hoses and wires. Question is...who makes this in a scale size? I would assume that the cranes turn on the bull gears, so there has to be a way that this works. Any help on this would be greatly appreciated! Thanks!