Q. 1. When did the Virgin Mary die? I cannot find any information on that subject.
A. 2 The Catholic Church has never proclaimed that the Virgin Mary died. According to Church tradition, at the end of her earthly life, the Virgin Mary fell asleep and was raised to Heaven while still living. The belief that she never died has its origin from the dogma of the Immaculate Conception, Mary being conceived without sin. Being incorruptible, having been created as the new Eve, she could not have died. For death is the punishment that plagues those who are born with the original sin. Mary was born without sin.
Q. 2. Where can I find some Catholic material to support what you are saying?
A. 2 I recommend you read the proclamation found on the Vatican website. It is called "Apostolic Constitution of Pope Pius XII, Munificentissimus Deus, Defining the Dogma of the Assumption, November 1, 1950.
I also recommend you read the Catholic teachings found in the Catechism of the Catholic Church, # 966, 974 and 484 to 511.