Some natives might know some secret locations....but here are my notes for laffy.
Not sure if these are the best but they are very good and plenty of inventory of everything:
http://www.donsspecialtymeats.com/ (Scott - just west of Laffy.)
Less selection but spicier boudin links from this place: Billeaud Grocery 111 E Main St, Broussard, LA, United States
I think this location is related: Billeaud's Too 1512 Weeks Island Road New Iberia, LA 70560
Some people swear by Billy's but I like the others better. (also in Scott and maybe other locations):
http://www.billysboudinandcracklin.com/
Earl's is good too. I've not had the boudin' there but there is always people lined up when I'm there getting lunch. https://plus.google.com/112980435165506046561/about?gl=pe&hl=en