I think you just need to look for the right term, "sourcebook" is usually used to denote a book comprised of source material. Such as:
I am not sure how much of any book is letters & how much is Roman historians or annalists documenting events mind.
Roman Imperial Texts: A Sourcebook https://www.amazon.co.uk/dp/B00FW7XAJY/ref=cm_sw_r_apan_glt_93D7GZ0KG3JRS52ZQKPX