Well, if you are using random maps, and the resource requires a unique starting tech to that Civ, and that tech is not tradable, you effectively restrict the resource to just that Civ.
If you are looking more for a historically accurate scenario with a map, you can preplace the settlers along side the resource. Or you can just "ballpark it", preplace them in the areas you want them to expand - depending on what that resource does they may fight for it.
I don't think you can organically restrict it to appear randomly within the civs borders, at least not in Civ3.