Lambda .Find on Index number to ID

I'm trying to do a simple find using Lambda..

Usually I'd do this:

this.Continents.Find((Continents c) => c.ID  == nations.regionID);

This usually works with no problem.

But I have a case where I don't have an ID value for Continents and its the index number which relates to the regionID...

For example:

In Continents I may have

Index number|String
[0] | Africa
[1] | Europe

In nations.regionID is may have

1
0
0
1

So using lambda I need to find based on the regionID to continent index number.