No, it's not a D&D magical item, it's an exploit.
A lot of hobos around the Junkyard have some fishing rods set up near the bodies of water next to them. Some of those fishing rods can be taken by the player (without even stealing them). Now, not only do these fishing rods sell for a hefty price (600), but the hobos seem to have enough on them to replace them every time you change zones and back.
That's right. Infinite fishing rods for infinite money.
Those hobos sure are generous.