The material you would add to your soil depends on which plants you are growing. For plants adapted to calcareous soils, nothing need be added, except the addition of air by rototilling compacted soils. Do not expect to see a response after mid-summer. After that time, the leaves are mature and will probably not absorb the missing nutrient.
Sulfur can burn a plant in the heat of summer and is best applied in the autumn or spring.
Fertilizers that acidify may be helpful but are not essential if other acidifiers are used. There are several acidifying fertilizers sold as lawn and garden fertilizers as well as for houseplant culture. They will specify a sulfur content on the label or will specify that they are acidifying. I suggest that you contact your local Cooperative Extension Service Office. The Extension Service Office is familiar with soil conditions in your county and with the various products sold in your county.