I want to let Gameboy fans know that currently, it's quite easy to purchase Lemmings for Gameboy online!
A used copy is available from Games Outlet for $19.99 US.
Wal Mart Online sells it for $19.96 US. I'm not sure if it's new or used. Wal Mart doesn't currently appear to ship internationally.
Hopefully Gameboy fans will be able to obtain Lemmings with either of the sources above.