In Diamond/Pearl, there's a hidden entrance to Wayward Cave under the Cycling Road.
You can get a Gible in there, but there are boulders in the way and you need to push them away.
Is there any way to get Gible before you can get Strength?
You can only get Gible in the bottom level of Wayward Cave in Diamond/Pearl, and that can only be accessed after you get the HM Strength.
Hope I helped!