My suggestion involves a small payment but it might be worth while. The Ministry of Defence publishes a magazine for British army personnel, simply called 'Soldier'.
I know that 'Soldier' used to accept small-ads from people seeking army penpals. (Indeed, the Ministry of Defence website directed potential penpals to 'Soldier' magazine). I assume that this is still true.
You can read the current edition of the magazine, by clicking through the pages, here:
http://viewer.zmags.com/showmag.php?magid=9163 0
(The text will probably seem very small in your browser. Remember that pressing the Ctrl and + keys together will make things bigger).
To enquire about advertising, phone 01252 347352 or email
[email protected]
(Alternatively, see if there's anything relevant in the magazine. I'm on a dial-up connection so I've not tried downloading the whole magazine)
Chris