Many the current T, X, P and even some L ranges are now 'certified' by Lenovo for use with Linux
The range of presently 'Linux certified' Thinkpads can be located here:
Earlier ('legacy') Thinkpads are listed here:
https://support.lenovo.com/us/en/solutions/pd500269
Where a Thinkpad has official support You can visit the suppot.lenovo.com page for the Thinkpad and select 'Drivers & Software' then 'order recovery media' and scroll down to locate a download link to and iso of the officially supported/certified version(s) of Linux for that Thinkpad