True it would have been taken away, but before becoming a padawon, younglings must first learn how to make a saber so whose to say he didn't make a new one after being banished, just my thoughts on it but it would probably be orange or yellow.
The only sources of Lightsabercrystals are under the guardianship of the highest security measure the Jedi can muster.
Pirates and others try to get to the crystals since countless decades for profit.
There is not much that is worth so much on the black marked than a kaydrin crystal. (just saw the clone wars episoder about it ^^)
When he was able to obtain a lightsaber than there is a very adventurous story behind that. Or he made enough money to buy one on the black market and that is nothing they have in stock every day so the opportunity as well as the money must have been given.
Hmm another thought. How about the other force user groups? The Jensaarai for example (one of my faves) are able to construct lightsabers somehow. They take more pride in their armors yet this would be a group where your charackter might have been able to obtain such a seldom weapon.
