Logos and Heracleitus (articles and books)
To find books go to COMCat and choose the Basic Search. Type in Heraclitus (watch your spelling) and select Keyword Search (any words) from the drop down menu. Hit enter.
For articles, EBSCO:The Religion and Philosophy Collection is your best bet. Choose the advanced search option. Type Heraclitus into the first bar and select SU Subject Terms from the drop down menu. In the second search bar, type logos and select TX All Text. Make sure the Boolen Phrase option is selected. You can enter the publication dates if you want to only include articles from a certain range of years. Click Search.
Also try EBSCO:World History Collection. Go to advanced search, enter logos as a subject term and philosophy as a subject term. You can narrow your results using the options on the left-hand side of the screen.