Whilst scouring the whole internet via Google search, I came across solutions for "Windows spotlight additional backgrounds" and additionally, I went looking for "Additional Screensaver downloads for Dual Screen use and installation".

1. Windows spotlight backgrounds.
Go into Windows 10 STORE.

Look for SpotBright. Freeware,but pay for paid version 79p, which gives you option to change hourly or daily both Lockscreen backgrounds (spotlight) and additionally, desktop backgrounds. You can download a vast quantity of backgrounds for Spotlight and desktop from here.

2.Site for screensavers that work on multiple monitors is ReallySlickScreensavers-0.2_installer.
Really Slick Screensavers - Downloads