Tax Codes & Tax Schedule

I are using the NetSuite C# API defined within the .wsdl at https://webservices.netsuite.com/wsdl/v2016_1_0/netsuite.wsdl.  With those definitions I am able to get Employees, Items, Accounts, etc.  I am not able to get Tax Codes or Tax Schedules.  You can see an simplified example of what I am doing in the following method:

public virtual ResponseObject GetInventoryItems()
        {
            ResponseObject response = new ResponseObject ();

            ItemSearchAdvanced searchAdvanced = new ItemSearchAdvanced
            {
                savedSearchScriptId = "customsearch_inventory_only"
            };

            SearchResult searchResult = Service.search(searchAdvanced);

            if (searchResult.status.isSuccess)
            {
                response.statusCode = Enums.OpStatusCode.Success;
            }
            else
            {
                HandleResponseError(response, searchResult);
            }

            return response;
        }

This all works because ItemSearchAdvanced exists in the .wsdl, but TaxCodeSearchAdvanced(or something like it) doesn't.  Am I missing something or is there another option I should be using to access Tax Codes and Tax Schedules?