The phrase "constant source" refers to something that is consistent and reliable in providing something, such as information or supply. It refers to a never-ending or unwavering resource that is always available. Full definition
These moments may seem to be constant sources of frustration — but so much learning comes with repetition. (mommyedition.com)
This week has been a nearly constant source of pain with only a few meaningful exceptions over the past 27 years (shaded in grey). (stocktradersalmanac.com)
These drawings have become a reservoir of knowledge, and constant source of information for making my paintings; very few drawings have ever been exhibited. (durdenandray.com)