This document explains how you can obtain a list of only the COM ports while using VISA Find Resource.vi.
You can do this by filtering through the VISA Resource Names returned by VISA Find Resources.vi. In a For loop, use VISA Open to open each resource, then use a Property Node to obtain the Interface Description (Properties » Interface Information » Interface Description). This property details whether a resource is a COM port or an LPT port. Using this information, you can discern which type it is with Match Pattern and a Conditional terminal. Use VISA Close to close the reference.
The below VI snippet shows an example of how to do this.