This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
There are many vendors. A few are listed below.
Incidentally, you have a lot of choices when it comes to CD packaging.
There are single-disc jewel cases, double-sized doubles, single-sized
doubles, triples, quads, sextuples, plain colors, neon colors, paper
envelopes, Tyvek envelopes, cardboard sleeves, clear jewel cases with black
trays, clear jewel cases with built-in trays, CD pockets for use in
three-ring binders, and on, and on.
If you can imagine it, it's probably up for sale.
Some URLs to start with:
A warning about some double-disc jewel cases sold by CompUSA can be found
at http://www.yoyo-tricks.com/CompUSA-WARNING.html (along with pictures).
Apparently the pressure exerted on the hub causes cracks to appear over
time. If a disc with a cracked hub is put into a high-speed drive, it
may shatter (see section (7-25)).