If Package Isn't Available on NPM

I'm trying to find best solutions for this. I've got a JS plugin that I need that doesn't seem to be available via npm. I usually require() my packages at the top of my app.js file so when it's spat out, it bundles all my js.

What best practices are there for when a plugin or package isn't available over npm or Bower. Are there any other ways to require() or is there a way around this?

I'd rather not have more than one js file on my site.

Any help is appreciated. Thanks in advance!