There are times in the life of every believer when prayer and fasting are "appropriate" - those times are not enumerated in Scripture:
Mark 9:29 And he said unto them, This kind can come forth by nothing, but by prayer and fasting.
1Cor 7:5 Defraud ye not one the other, except [it be] with consent for a time, that ye may give yourselves to fasting and prayer; and come together again, that Satan tempt you not for your incontinency.
In the Mark passage, Jesus tells his disciples that there are times when they can accomplish something (in this, casting out demons) only through "prayer and fasting."
In the Corinthians passage, the Apostle Paul tells his readers that there are going to be times in the life of a married couple when they are to cease from their normal activity as a couple to devote themselves to fasting and prayer...but that is not all the time, and it certainly doesn't specify a certain "season" - but when it is appropriate.
Now, having diverted attention from the original question, where in the Scriptures are "Mardo Gras" and "Lent" identified?