Silent Service 1 + 2
 

Apologies if this isn't news, but SS 1 + 2 are on GoG for about a quid.

GoG games

That's where I got my copies when they had another sale back in 2014.

They install automatically and somehow come with DOSBox already configured for them. Both are an easy install and fire right up from shortcuts on your desktop if you like. I'm running Windows 7 x64 SP1.

Prior to discovering GOG I ran SILENT SERVICE 1 from a ROM through a NES emulator. ROM's for various platforms like NES, SNES, Atari etc. are hard to find nowadays because the gaming companies got the rights after they found a new market with smartphones & tablets.

Edit: apparently ROM's are freely available online again.... hmm.
Example: http://www.freeroms.com/nes_roms_S.htm

They dried up in the late 90's. The Emulators have always been easy to find, and they are usually free.