http://www.radio-locator.com has listings of radio stations in US and Canada I believe.It
now has lists of HD2, HD3 etc channels on the pages of the main stations.At least a couple Boston stations I checked, WGBH and WJMN have their subchannels listed.The pages are linked to the "info" button when browsing areas, etc.
Example
https://radio-locator.com/cgi-bin/finder?call=Wgbh&x=16&y=1&sr=Y&s=C
HD Radio's site does list HD stations but can often be outdated.
now has lists of HD2, HD3 etc channels on the pages of the main stations.At least a couple Boston stations I checked, WGBH and WJMN have their subchannels listed.The pages are linked to the "info" button when browsing areas, etc.
Example
https://radio-locator.com/cgi-bin/finder?call=Wgbh&x=16&y=1&sr=Y&s=C
HD Radio's site does list HD stations but can often be outdated.