Trouble finding an NJM2360D Boost Converter EAGLE library
It is likely that you won't find a library for specific parts such as this. In the datasheet for your part, you'll find a "footprint" or "land pattern" or "mechanical dimensions", etc.

There are many tutorials for how to make a symbol and footprint in Eagle. If you're going to be designing a PCB, I would recommend you take the time to do this.

For your first footprint, I would suggest drawing it out by hand and calculating the dimensions once or twice to be sure you're correct. There is nothing worse than getting the PCB back to realize that your part doesn't fit.

Another recommended strategy is to print out your PCB on paper before ordering.