In recent Typescript it defaults not found modules to type `any` and only complains if `--noImplicitAny` is used.
Even with `--noImplicitAny`, it's gotten pretty easy. Leave a scratch .d.ts file somewhere in your project and when you install a new library you can start with:
declare module 'libraryname'
declare module 'libraryname/**/*'
That gives you an explicit `any` for those libraries. Then you can go back and add types later.
The number of npm packages with types directly included is growing at an impressive rate (even Facebook often bundles them for React libraries), so there's not even the need to seek out types in so many cases these days.