You can do things like grab a few handfuls of soil from a wooded area around you that will up fungal counts for the most part. Any type of high carbon based compost or worm castings will have a higher count of fungi in it so compost or worm bins made with lots of dried leaves etc would produce a good fungal counts if the other conditions are right. Bacterial microbes will feed on a food source like molasses or a sugar based feedstock where as when I want a higher fungal count I use things like yucca or seaweed extract. Fungi do better with more carbohydrates (cellulose) or simple proteins. I do different brews for different things. Potted or raised beds with quality soil I do bacterial since the plants will usually get more out of it but in sandy soil or more long term for pasture improvement I use fungal teas. I add several meals and soil amendments along with castings, frass and a feedstock for the brews and sometimes I do basic castings and feedstock.