Final Fantasy III/Crystal Tower

Onion Knight equipment (NES)
Here is where you can find the Onion Equipment. All the five parts are dropped by Dragons.

In the NES version, dragons appear four times every 256 battles.

The first dragon appears after about 128 battles. If you already got the treasures of Eureka, that means: leave the Invincible, cross the Ancients' Maze, walk to the bottom of Eureka, then to the 7th floor of the Sylx Tower, back down to the 2nd floor and start climbing up again. The second dragon appears after about 64 more battles, that is another visit to Eureka (buy tens of Shurikens) and back to the Sylx Tower. The third and fourth dragon appear after about ten more battles each. Forty more battles and the cycle starts over, that is you need 40+130 (=170) more battles to meet another dragon. Better go back to the Invincible, save game and reset the NES.

The dragons drop an Onion part only if they are hit by an instant-defeat spell. There are six: Breakga, Death and Warp from the black magic; Mini, Toad and Exit from white magic; petrifying hits from Omnirod and Golem staff count as well. You should better defeat the dragons on the second turn, or maybe a later one, for a better chance to get an Onion equipment part.