Hello!
I am not aware of any specific group that provides webinars about mechanical engineering, but you may find some free webinars and online courses related to mechanical engineering on websites such as Coursera, edX, and Udemy. You can also check out the website of renowned universities to see if they offer any free online courses regarding mechanical engineering.
Additionally, some organizations such as the American Society of Mechanical Engineers (ASME) offer webinars on various topics related to mechanical engineering, but they may require membership or a fee to participate.
I hope this helps, and feel free to let me know if you have any other questions!