What follows is more of a personal opinion.
NetBSD supports over 30 different architectures and attempts automated packages builds for
all of them.
The binary builds utilize their pkgsrc system which has quarterly releases and 2013Q3 is current at this time. So port maintainers submit their updated code to a quarterly release which the build system utilizes to make binary packages. As you can expect, not all packages build but while a quarterly release is active there are tweaks to the build code to allow more packages to build.
With that background:
1) Build it yourself from pkgsrc
2) Wait for the build system to produce an mplayer-share package. Not guaranteed to happen - some complicated packages, eg. a native libreoffice, have yet to build and others build but do not run.
3) Try an earlier build ie 2013Q2 - caveat: You will get into trouble if you mix 2013Q2 and2013Q3 packages.
I would recommend looking a the NetBSD mailing lists,
Pkgsrc.se and perusing the ftp sites:
NetBSD FTP sites. In your case you would find mplayer packages absent but that vlc packages compiled sucessfully.