I ended up injecting the content type service (IContentTypeService) and using that to get all the content types. Looping through the list, I got the content type alias of each item and used the aliases to get the all content (published/unpublished). Here are the code snippets:

Get all content types:

var allContentType = _contentTypeService.GetAll();

And then get the alias (and use it):

            var contentList = new List<ISearchResults>();
            foreach (var contentType in allContentType)
            {
                orderedExamineQuery = searcher.CreateQuery(IndexTypes.Content).NodeTypeAlias(contentType.Alias).OrderBy(new SortableField[] { new SortableField(DocumentTypeConstants.PropertyAlias.PostDate) })
                    .Execute();
                contentList.Add(orderedExamineQuery);

            }