Do any nested or multi-level responsive menu components exist, either for free download or purchase? As Frameworkless components go, I'm only finding single-level, and the Mega Menu is not responsive. Appreciate any help you can lend!

not as components if you if you are using frameworkless

You need to build one from scratch and would probably need to introduce some custom made CSS or JS stuff ( Frameworkless comes with just the bare bones stuff)

However one of the CC Users called Inger has made some components for Frameworkless that includes some nested menus, you can download and insert into your project

Her page is here
https://mock-up.coffeecup.com/#tab-panel-4