[quote="jtodisco, post:2, topic:311380"]
Can. 1190 §1. It is absolutely forbidden to sell sacred relics.
§2. Relics of great significance and other relics honored with great reverence by the people cannot be alienated validly in any manner or transferred permanently without the permission of the Apostolic See.
§3. The prescript of §2 is valid also for images which are honored in some church with great reverence by the people.
Additional information on obtaining relics of various classes:
I don't think the OP was suggesting that he/she wanted to actually buy relics, which of course is forbidden.
The major relics that can't be moved without permission (what Canon 1192.0 refers to above) are the big ones - like the whole body of a saint, or an arm, or the Crown of Thorns, etc. Not the little tiny ones that you usually see.
However, the office in Rome that typically distributes relics is not doing so to lay people anymore, since there is so much abuse these days - people selling them on ebay, which is simony and a mortal sin, etc. etc.
Sometimes the promoters of a person's canonization cause will distribute relics, but this is pretty rare.