OTC for over the counter
In france you can buy some antitussive medications such as neo-codion, paderyl, tussipax etc. without prescription : those are pills with about 20 mg codeine in each (to buy 30 mg codeine pills you'll need a prescription which is quite stupid and useless). You can't buy more than a box at once but each contains a total of about 350 mg codeine which is more than you need. In big cities you can often notice empty medication boxes lying on the streets...
After doing some research it seems that in holland (and america) codeine is under "heavy control" (personaly i'd prefer to have free access on weed and more restrictions on codeine)
Maybe there is another way for you to get codeine :
You have to go to any epicery or store where they sell poppy seeds : it is used in cooking (bread, cakes). You'll need 300 gr of seeds : it's quite cheap. Make a tea (among other opiates alcaloids your tea will contain codeine) : grind the seeds, add water, lemon juice, stir, let sit for a couple of hours & drink.
Aim less than 300 gr of seeds for the first time, beware : codeine is addictive, nauseous and you can overdose on it.