Sorry, but there is something wrong with you story: If count Johann Karl Harrach is your great-great-great-grandfather he must have lived in 1750 - 1800. But this is 150 - 200 years away from the 30-years war.
Your Karl, First Count of Harrach, died in 1628. He had 9 children, 6 sons and 3 daughters. So there are some generations missing (about 6 - 8) in your ancestry-line.
The problem is also, that you will never find a child of Johann Karl, because he was not married. He only could have had illegitimate children and this children never had the right to wear the title Count. But it is very improbable, that a illegitimate child would have been named after his father with "Harrach". I think it would be better, to research first the ancestry line step-by-step.
In Breslau there was an infantry-regiment "Harrach" in the 7-years war. Maybe the father of your first Harrach was a soldier there and so the name "Harrach" was created in this way. Or - what is very possible - that the first Harrach was so called "Hofjude" (jew at the court) of the Harrachs and in the end of the 18th century - when all jews had to get a last or family name - he was allowed to wear the name of his lord. For this, i know a lot of examples like Waldstein, Schwarzenberg, Liechtenstein etc. etc.