Why is the number ranging from 50-300, isn't it pretty low for such a huge forum? Are there only 300 reputed members? May be you could give around 1000-2000 coins to all those willing to expose their location to you primarily since most of them remain anonymous. Also what would be the purpose of giving someone a collectible coin (which might be quite rare) if they doesn't know what it is?
50-300 is fine.
If we do not state a definite upper limit then we run into a Sorites paradox, where n+1 is as good as n and hence we arbitrarily increase.