CBS streams all theirs via their radio.com phone app. Last I checked, they don't list their HD channels (i.e. ROQ of the 80s) on TuneIn, but anyone who knows the naming conventions of these streams can just go to the TuneIn site and save the custom stream there. That's what I did, since I had no use for the radio.com app.
Other companies also stream their HD2 channels. One example is The Drive in Chicago.
Clear Channel maintains a stable of music format channels, such as Alternative Project, for their IHeartRadio app (which is the streaming app I recommend to people the most, due to its simplicity, stability and versatility). For HD2 streams, the stations just plug 'em in.
However, there are some exceptions that don't stream. I believe KSHE in St. Louis has a custom HD2 channel that does not stream, and can only be found via an HD Radio tuner.