No CDN Solution

[xiaohutai]

A solution without CDN depends heavily on your workflow. Here's a quick reference if you use NPM.

NPM

Install the packages using NPM:

npm install leaflet
npm install leaflet.markercluster

CSS

The locations of relevant CSS files:

node_modules/leaflet/dist/leaflet.css
node_modules/leaflet.markercluster/dist/MarkerCluster.css
node_modules/leaflet.markercluster/dist/MarkerCluster.Default.css

JS

The locations of relevant JS files:

node_modules/leaflet/dist/leaflet.js
node_modules/leaflet.markercluster/dist/leaflet.markercluster.js

Finally, concatenate and minify using your available tools (Gulp/Grunt/Parcel/Webpack/...).