Apple pulled Mojave 10.14.0 -- Where can i get it? -- 10.14.4,,,10.14.6 etc., are still available from Apple
If you can't install macOS Mojave, your Mac may not be compatible.

First check the requirements on Apple Technical Specifications. Then, you can manually download the installer through Apple Official Support or the Mac App Store.

If you still can't update to macOS Mojave, you may download the installer from an external source, like I did when I needed to update from Snow Leopard (10.8) to El Capitan (10.11).