Apple decided to remove telnet and ftp from high Sierra. It is understandable , because they are not secure. But some of us need it for old systems, or local machines. I was able to go back into an old version of Yosemite and copy those two binaries into my current system. They are available on this page. You will need to copy them into your /usr/local/bin/ folder.
MD5 (telnet) = 89720c99bbdb96fdfa7f13fdc4bf0a07
MD5 (ftp) = dea942a96a3758a275b70b3f3915abda