If I'm not mistaken, 1099's are only required for amounts of $600 and above - which is why you probably haven't received one.
I believe the minimum is $10, not $600.
Is it possible that the $300 is not "interest". I.e., that it is categorized some other way? For example, we get a few hundred dollars a year bonus dollars from credit cards. It is never reported to us on a 1099-X form. I've actually never even considered it might be "income" in the eyes of the IRS until this moment.