Are you using useGalaxy.org? The main public instance of Galaxy useGalaxy.org) does not host proteomics tools, though, setting up a local Galaxy instance or Cloudman instance will allow you to install proteomics related tools from the toolshed.
If your goal is to simply create a workflow with proteomics tools, you can use https://usegalaxyp.org, which is an instance established by the Galaxy-P group at the University of Minnesota for users to create and share workflows for proteomics analysis.
Hope this helps! Please feel free to respond with any questions.
Thanks for using Galaxy!
Mo Heydarian, Galaxy Team