Yes, Vernier does sell a Goniometer.
Goniometer (GNM-BTA)

However, if you already have our Low-g Accelerometer, you can use it to report tilt angle using our Logger Pro 3 software.

The JointAngleSensorLowG.cmbl Logger Pro experiment file is configured to use the accelerometer in this way. Using this file, Logger Pro 3 will report an angle of 90 degrees when the accelerometer is resting flat. As the accelerometer is tilted is will report a decrease in angle.

To create your own file in Logger Pro 3 setup the following:

• Create a calculated column that takes the ArcCos of the Acceleration reading divided by g, the acceleration due to gravity. [ArcCos(“Acceleration”/9.8)]
• Make sure that Logger Pro is using degrees for all trigonometric calculations. The default setting is radians. See ‘settings for file’ under the the FILE drop down menu.
• For the Data Collection settings, sampling at 10 samples a second works fine and some smoothing should be used as well.

Vernier also sells a Rotary Motion Sensor that can be used as a goniometer. You will need to attach a rod to the Rotary Motion Sensor and then place the Sensor on the joint of interest. Once again, you will need to make sure that you are using degrees for all trigonometric calculations.