Descriptive grammars lay out the grammatical elements and rules of a language as it is actually used. Descriptive grammars are written by linguists who study how people create and use a language. Don't confuse descriptive grammars with pedagogical or prescriptive grammars. Those are the books that teach how a person should use a language following an idea model. All those "how to learn x language" books are prescriptive. For more on this difference, check out these web pages:
Most academic libraries organize grammars by their language, which means they are not in the same grammar or linguistics section, but instead they are spread widely across all the various languages. EMU Library and many others organize their books using the Library of Congress system. Here's what it looks like for languages and linguistics: https://www.loc.gov/catdir/cpso/lcco/ (click on "P" to see all the subsections). As a result of this, if you want to compare or select among descriptive grammars, you might have to do some walking around to get from, for example, the Germanic languages to the African languages.
How to find a descriptive grammar of particular language: All descriptive grammars are given the subject tag of X language--Grammar. So, if you have a particular language in mind, here are the steps:
How to discover descriptive grammars of any language: This is more difficult, and you will have to do some sorting through results.