My work is on microscopic image based identification. So I need a fungi affected microscopic leaf images of any plants for my research work. Below is a sample image for reference. Any site or repository or any sort of help is appreciated. Thank you.
I think it is possible for you to find these types of images in many papers, especially those published on foliar fungi/ plant pathology and fungi associated with different tree species.
There are many references deal with fungi classification such as: The genus Aspergillus, Compendium of soil fungi, Fungi and food spoilage, The genus Penicillium, etc..
You appear to be asking where you can find images of disease symptoms on leaves, rather than of cultures and microscopic details as in your images. Try plant pathology textbooks. The American Phytopathological Society published a well illustrated Compendium of Wheat Diseases [1977]; they also did Maize and Soybean. There may well be others since then. Check C. Westcott's Plant Disease Handbook reprint of the original 5th ed. 1990 - I'm not sure how well illustrated it is.
Most of papers which published on plant fresh system (foliar group) diseases and the text books of plant pathology contain hundreds of images for the symptoms of different plant diseases. But you must depend on the identification of these pathogens depending on the identification keys besides the noticed symptoms. So, the symptoms alone are not enough in my opinion.