Trainers for such a thing are VERY difficult, Weasel; there are no obvious values to search in memory for such a thing, so it takes serious skill to undertake an effort like that. It's usually easiest, with a trainer, to look for numerical values; this is why all but the most advanced trainers usually affect things like HP, ammo, money, etc; they're numbers that you can find.

You might be able to figure out which values determine if a collectible's already obtained, but if they're not using a straightforward 1/0 value to track it, then it might take hours, with no promise of a payoff. Too much work, especially when finding a change in the value is dependent on a randomly generated collectible, which may not be the value you're trying to track.

I'll see, though, what I can do about the random number generator the game uses; it might be possible to locate that with a trainer as the game is running, and influence the outcome. However, due to policies on the boards, I won't be posting them on the forums. I'll post if I found a system that works, but I won't post details publicly.