After a bit of research. Normally Microsoft will only support Windows 10 build 1607 until April 2018, but Microsoft has reported they will continue to release security updates for Clover trail devices only.
As for the ISO, I did find this site which has download links to the older builds. Downloading the ISO itself from a third party site while legal, may have some extra fluff slipped in, so I would be sure to compute the hash after the download and check it below to make sure they match
Link Removed
File names and SHA1 hash values:
Edition: Windows 10, product language = English
Windows 10 English 32-bit download
File name = Win10_1607_English_x32
SHA1 hash value: 5a4d2c953d884578a6adb448bee5753b80ec1cfa
Edition: Windows 10, product language = English
Windows 10 English 64-bit download
File name = Win10_1607_English_x64
SHA1 hash value: 99fd8082a609997ae97a514dca22becf20420891