I have used the services of several well known MBS data sites that are primarily subscription based. In my experience, I have found the information on Mortgage News Daily’s blog to be the most timely information with the most frequent updates.
Since I utlize the data on Mortgage News Daily every day, several times a day I know from experience that the data is extremly timely.
Here is the link http://www.mortgagenewsdaily.com/mortgage_rates/blog/ I may be biased but no other site comes close in terms of timely data.
You could also google the topic and find several other credible sites that contain and psot MBS data.