Single-Case Design studies are very common in Special Education & Communication Disorders, so as you get used to reading them weeding them out will become easier. Here are some tips to help as you start your research:
Include terms like "single-case," "single subject," or intervention as keywords in your searches. Most articles include methodology in the abstract, so this should help those rise to the top or your search results.
Examples of searches:
A classroom teacher wants to find examples of single-case design research that studies the effect of praise on reducing disruptive behavior.
"praise" AND "classroom behavior" AND "single-case"
A school psychologist wants to find research about single-case experiements that studied intervention programs for students with autism.
"school intervention" AND autism AND "single case"