I don't see the original AM-14U on AM anymore. Last year's model, the AM-14U2 is still available (we purchased two earlier this month; we're 95%+ likely to use these for our competition and practice robots for Stronghold). If you go to
the AM-14U2 page and click on the "Files and Documents" tab, you can find links to CAD STEP files for various configurations. When the "U3" is released (probably immediately after kickoff), I expect those CAD files to be available as well.