For free options there's FreeRADIUS, but that's going to require you to build and manage a server to run it on. I'm not sure if they sell an appliance... They do sell services though.
For paid solutions there's products such as Cisco ISE, and Aruba ClearPass. Both are available as an appliance.
There's also cloud solutions like JumpCloud or Duo that are more IAM but have RADIUS functionality. These may also work for you.