I have experience working with the Telegram API and would be interested in discussing this project with you. A simple Node.js script should achieve what you've after with a couple of hours work.
Assuming you wish to send messages via a bot rather than as your user, the script would have configuration options to set up a bot user (I will supply a tutorial if you need it). You could then provide a file with a list of names, which would be resolved to their Telegram ID's. It would then be able to send the message you supply (either by file or commandline - your choice).
I need a little more information, but this sounds like a relatively fast project.