Find articles about the language you're hoping to study and watch the citations in those articles.
Often you'll find citations to a relevant corpus or dataset.
In library searches, the word "Grammar" applies to two things: a core linguistics work that describes and provides examples of a particular language, and a school child's guide to learning a native language. There's no good way to distinguish between those two in your searches, but here's how to find what you really need:
This technique also works in WorldCat.
Many linguists publish their findings on the web, either in collections like OLAC, through organizations like SIL, or on their own researcher websites. Here are some of the best ways to find that scholarship: