Microsoft still hosts some SDKs and update packages on their Official Download Center , though these are not full OS ISOs: Windows CE 5.0 Live CD - Internet Archive
By focusing on your specific hardware or the official development toolkit, you will avoid malware and actually get your legacy device running again. Windows CE 5.0 may be dead, but the machinery it powers is still very much alive. download windows ce 5.0 iso
This is your best bet for abandonware. As Windows CE 5.0 is no longer sold or supported by Microsoft, many users have uploaded ISO archives to archive.org . Microsoft still hosts some SDKs and update packages