You can watch NHRA Stock or Super Stock run live during NHRA Division 3 events on D3TV (a YouTube channel). The NHRA Div. 3 Facebook page publishes the daily schedule of runs / classes so you can follow along on D3TV.

You can see the NHRA Factory Stock Showdown on the web live on NHRA All Access (web based video streaming) but it is a subscription service. You can pay for an event or the whole season. You can also watch a recap on the Fox coverage of the NHRA events where Showdowns are run (5 events in 2017, 7 events in 2018).

Lastly, you can watch these cars run in Factory Supercar at NMCA events on SpeedVideo (another web based video streaming channel) for free.