Hello,
You will have to go to websites like the Internet Archive to get the ISO. With this being said however, your experience will probably be lackluster due to the fact that it's a beta therefore causing you to be unable to use it reliably.
I hope this information helps.
Disclaimer: The website mentioned is a non-Microsoft website. This page appears to be providing accurate, safe information. Please watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.