I don't know the particulars of why Lee Tracy didn't get that role. At the time he wasn't under contract to any studio. He had briefly been with Fox Studios but then went back to the stage. The Front Page was distributed by United Artists. I'm also assuming there was more interest in backing someone like Pat O'Brien who garnered a lot of leading roles after starring in "The Front Page". I think another factor is that Tracy also had a bit of a reputation as a drinker and a troublemaker.

In regards to "Blessed Event", that really is his best film. It was released on VHS many years ago, so maybe you would be able to find it? I'm assuming it will never get a DVD release as it's probably one of those movies that no one knows who owns the DVD rights so it just languishes in a vault somewhere, a shame really.

I love TCM, even though lately their idea of "classics" doesn't always jibe with mine.