If you buy the 2 CD version of 'Killers' on Castle Records, 'Maiden Japan' is on the bonus disc. This is out of print, so you would probably have to get it on eBay.
Paul DiAnno is pretty good live on these tracks, so if you get a chance, I'd pick it up. Also, the Killers w/Bonus Disc also has "Women In Uniform" on it. I'm pretty sure this is the only place left on CD to get it from...
Maiden Japan was also available as part of the "First Ten Years" boxed set of CD singles......It was included on the "Purgatory" disc. Might be a bit tough to find in that particular format.