Is it obligatory for one who missed congregational prayer due to an excuse to seek out another congregation to pray with?

Congregational prayer is an individual obligation (fard ayn) upon free, adult men who have no valid excuse for not attending it. It is not a condition that it be performed in the mosque, although the mosque is better.

If you miss the congregation due to an excuse, you are not obligated to go to the mosque to search for another congregation. It is sufficient for you to pray in congregation with some of your family members at home.

If you do not find anyone to pray with in congregation, and you know that you will find a congregation in the mosque, then you must go there.

Making an effort to go to the mosque to attain the reward of praying there, or to join a larger congregation, or going to a further mosque to catch the congregation, is praiseworthy (mustahabb).

Al-Aswad and Anas went to another mosque to catch the congregation, and Layth ibn Abi Sulaym used to search for a congregation in other mosques if he missed it in his neighborhood mosque.

Imam Ahmad explicitly stated that whoever misses the congregation in his neighborhood mosque should go to another mosque to catch the congregation.