public static ElementType GetFamilySymbolByFamilyAndSymbolName(Document doc, string familyName,
string symbolName)
{
var collector = new FilteredElementCollector(doc);
FilterRule rule = new FilterStringRule(new ParameterValueProvider(new ElementId(BuiltInParameter.ALL_MODEL_FAMILY_NAME)),
new FilterStringEquals(), familyName, false);
ElementParameterFilter elementParameterFilter = new ElementParameterFilter(rule);
var elementType =
collector
.OfClass(typeof (ElementType))
.WherePasses(elementParameterFilter)
.OfType<ElementType>()
.FirstOrDefault(x => x.Name.Equals(symbolName));
return elementType;
}