How do I get drivers for Windows 10 x64 installed on my Mac?
Remove the partition and installation you made and go back to the BootCamp way. Then, inside the Windows installer, format the partition BootCamp makes for you, that is an extra step that is needed. Then, you can install Windows 10. I'd suggest using a USB stick to prepare the Windows 10 installation so that Drivers are included automatically.

If you do not want to follow this strategy, there is an option to download the BootCamp drivers separately, either from Apple's site, or from within the BootCamp utility on OSX, from one of the top menu's or the default assistant screen. The menu is called Action and has only one option: Download Windows Support Software. Once you have it downloaded, copy it over to a FAT32 USB stick so Windows can read it and your Mac can write it. exFAT might possibly work too. Reboot in to Windows and then open the bootcamp setup program form the directory you just downloaded and follow the on-screen steps.