If you own a copy of Avalon Hill's Submarine, they have solitare rules here. That's a great tactical WWII subsim. Sub vs convoy. It also has a link to buy used copies.
http://doniphann.net/tsculler/
I don't know if what you're looking for specifically exists, but the best place to check and ask around is the wargame forums here:
http://www.boardgamegeek.com/
Someone here is BOUND to be able to point you in a direction and maybe even answer your questions about Silent War more precisely.
There's a fun little travel sized WWII solitare convoy game here for downloading and printing. It's actually fun to take with you on a long trip (I've played this quite a bit on trips while my wife was driving). All you need is print outs of the playing sheet, a pencil, and 1-2 six sided dice.
http://www.angelfire.com/games2/warpspawn/MaltaC.html