I've checked on Wikipedia and other biographies on Beethoven but I can't seem to find any other masses he did apart from the one in C Major. Does anyone know any others or even better, could someone refer me to where I can find more.
Beethoven wrote only one other Mass: the Mass in D Major, Op. 123, called the Missa Solemnis (Solemn Mass). It was premiered in 1824 in St. Petersburg, Russia. It was written around the same time as his 9th Symphony. While it was considered to be a great achievement, the earlier Mass in C, Op. 86 from 1807 has proven more popular over the years.
Beethoven wrote a German-language sacred oratorio, Christus am Ölberge, Op.85 (Christ on the Mount of Olives), to a libretto by Franz Huber. It is Beethoven's only oratorio. It was not considered successful and is rarely performed.
Beethoven, historically, was a notable example of a great composer who earned his own way without relying on patronage; that is to say that he did not have a period of his career where he worked full-time for a church, a ruler, or a nobleman's court. That may be why he wrote relatively little religious music. Many well-known composers before him wrote a great deal of church music because they were specifically commissioned to do so by their employers on a regular basis.
To find a large list (not completely exhaustive) of compositions by any composer before the 20th century, always check the listings at imslp.org, the International Music Score Library Project. They provide free downloadable scores for a great deal of music that is in the public domain.