Looking for primary source materials for a topic addressing a non-English speaking country and you can't read the language? Books will be your best bet, because they are the most likely place to find translated sources.
Here are some examples of primary sources frequently found in book format.
Works of historians or other writers from the time periods of the HRE in translation
Individual or collected diaries/memoirs
Letters and/or papers of individuals
Collected documents on the same topic and/or from a time period.
Tip: I have found that many of these books will often include one of the following words in their title: sources, documents, or documentary. Try adding one or more of those to your search to keep the focus on finding collections of primary sources.
Images of physical artifacts (think things like collections of inscriptions, art, or other archeological artifacts)
Here are some examples of books containing primary sources.