"Rocman X," the infamous NES pirate is now available to play online for free at Nintendo8 Online.
It's a strange pirate indeed, baring little resemblance to the source material with a few tidbits that reek of rip off. (yes, the title is actually spelled "Rocman X", not a typo.)
Periodically, you can find a hard copy of the game on ebay under the name "Thunder Blast Man" or "Sachen," usually from anywhere between $15.00~$30.00.
You can learn more about Rocman X here.