Th following line is from the market_misc.ini file
MarketGood = torpedo01_mark02_ammo, 30, -1, 50, 50, 0, 1
The number 30 represents the required level to buy the weapon.
Change it to what ever you want . Only catch is that it has to be changed at every single location.........oh the agony of repeition.
So, make it look like this:
MarketGood = torpedo01_mark02_ammo, 0, -1, 50, 50, 0, 1
.....and you can buy it right from the very start of the game.
Also note that the second number (-1) denotes your reputation requirement with the operators of the base in order to buy.
-1 = enemy or better in other words any one can buy
0 = neutral or better
1 = must be friendly to buy, in the green on rep scale seems to be enough