Here are a couple options.Python:
import arcpy
arcpy.env.workspace = r"[Path to an SDE connection file goes here]"
featureClasses = arcpy.ListFeatureClasses("G*", "ALL")
for featureClass in featureClasses:
print featureClass
C# / ArcObjects:
IWorkspaceFactory workspaceFactory = new WorkspaceFactory();
IWorkspace workspace = workspaceFactory.OpenFromFile("[Path to an SDE connection file goes here]", 0);
var namesEnum = workspace.DatasetNames[esriDatasetType.esriDTFeatureClass];
var tempName = namesEnum.Next();
while (tempName != null)
{
// Add string comparison logic here, e.g. tempName.Name.StartsWith("G")
Console.WriteLine(tempName.Name)
tempName = namesEnum.Next();
}