Do you mean a chart for a specific coin with a graph of value over time?

This sort of graph is more for speculators on financial products. You can find these things for gold and silver and other assets like that, but numismatic value of coins tends to be pretty stable unless there is some change in the market (which there are sometimes).

So if you were to use any of the man price guides for coins, you'd see they trend upward, because of inflation, and some go up because of their popularity increasing, or a market adapting to new information.

But numismatic value is a poor thing to "invest" in. It is a hobby and one would be better of relying on metal markets or something else not driven by a hobby.