NBC Sports Radio is no longer a 24/7 network. It supplies brief sports updates to stations but only has a few full length shows. I'm not sure where it can be heard other than a few sports stations around the country that use it to supplement a 24/7 network. And it supplies updates tailored to Bloomberg Radio.
The 24/7 Sports Networks....
--ESPN
--Fox Sports Radio
--CBS Sports Radio (now owned by Entercom and soon to change its name)
--SB Nation Sports (formerly Yahoo, Sporting News, One on One)
--ESPN Deportes (Spanish - disbanded last year)
--TUDN Radio (Spanish - formerly Univision Sports Radio)
NBC had a good product. In some markets such as Phoenix and Las Vegas, there were four all-sports stations and NBC Sports Radio was heard on one of the stations. But that wasn't enough.
ESPN got there first, years before the others. Fox was second. And then CBS and NBC arrived at the same time in 2012. But CBS Sports Radio was backed by Cumulus, which uses it on most of its sports stations. NBC had no such deal and was all but disbanded last year. SB Nation has always been content to be heard in Houston on a co-owned station, and be the last sports network among affiliates around the country.