Today, I am going to be addressing… something. People act like there is no explanation for Maz getting the lightsaber and acting like it is a plot hole, acting like the lightsaber was dropped into the atmosphere of a gas giant, never to be seen again.
Firstly, this acts as though it were implied, shown or made clear in The Empire Strikes Back that the lightsaber did fall into Bespin’s atmosphere after Luke had his hand sliced off by Darth Vader… except there was no indication that the lightsaber did fall out of Cloud City and into Bespin’s atmosphere, never to be seen again.
Secondly, there is an explanation in The Force Awakens alone. It isn’t explicitly spoon-fed to you; instead, it relies on inference, like almost everything else in the sequel trilogy.
We know Maz is not only friends with Han Solo but is also familiar with the history of the lightsaber (she had to have received this information from Luke, he is the only other person to know about this), and the fact alone that she found the lightsaber implies she is familiar with Bespin — one can infer that Maz went out to find it and eventually came across it at the bottom floor of Cloud City.