This particular badge is pretty rare (especially outside Japan).
Personally I don't recall a single sale of this badge on eBay in a last few years.
In general navy proficiency badges are much more rare than army badges.
Among army and navy badges the must common is marksmanship/sharpshooting badge.
I think it will be fair to say that army sharpshooting badge can be bought at any given moment (or almost at any given moment )
All others badges are much more scarce.
Constantly monitoring eBay section devoted to Japan you will be able to find most common army proficiency badges and some of these 2nd class navy badges (sometimes even cased 1st class! http://www.ebay.com/itm/Very-Rare-NAVY-1st-CLASS-WIRELESS-PROFICIENCY-MEDAL-JAPANESE-JAPAN-BADGE-/360741727203?pt=LH_DefaultDomain_0&hash=item53fde1ebe3 )