Install BootCamp drivers Windows 10
NEW SOLUTION

Open Boot Camp Assistant, and click on "Action" in the menu bar.



Click on Download Windows Support Software.

OLD SOLUTION

You can download the drivers from Boot Camp Assistant.

First, uncheck "Create a Windows 7 or later install disk" and "Install Windows 7 or later version", leaving only "Download the latest Windows support software from Apple" option checked. It should look something like this: 



Make sure you have a USB drive connected, and click continue. You should see a screen like this: 

. 

Select your drive and click on continue. It should download it to the connected USB drive.

Reboot into Windows, and install the support software from the USB.

Edit: I found Brigadier, a software that fetches and installs the drivers for you on Windows. I'll take a look at it, when I have more time.