While Google Scholar is a better option than Google when conducting a literature search, Google's algorithm for finding resources works really well when searching for guidelines, even when you don't know which organization has developed the guideline. The best way to search will be to put in the disease name and then guidelines (e.g., hypertension guidelines). If you know which organization's guidelines you would like to use, then you should include that in your search. If you are looking for the organization's guidelines, then it is best to put in the organization's name and then guidelines (e.g. American Heart Association guidelines). This will often provide a direct link to the guidelines page. 

When searching for guidelines, Google will show a variety of links. It is better to go to the organization's page where the link to the guideline is housed rather than a direct link to the PDF. This is to ensure that you have the most up-to-date version of the guideline. This is especially true for newer/more recently updated guidelines as those links may be lower on the search results list due to Google's search algorithm.