Kathleen:
 
I have been in Fiji a number of times, usually enroute to other islands,
but normally spend a day or so there.
 
About 25 years ago, we found quite a few shells snorkeling off a number
of beaches, particularly near Korolevu.  The highway often is far from
the shoreline and not easy to get to the beach, but we always found
someplace and some shells. (The highway at the time was an endless
string of potholes).
 
The highway has improved drastically.  However, 15 years later in the
same places even the common shells were very much more scarce.
 
In the last few years we have stayed at Taveuni at the Garden Island
resort and enjoyed it.  There were quite a few beach shells, and some
shells snorkeling, particularly at a small island off the resort.  My
main camera broke, and I make photographic trips so mainly touristed.
 
Also spent a week on Kandavu, found some shells snorkeling and some
diving, but not fabulous.  Generally, I haven't found shells to be
abundant at any of the places I have been in Fiji in recent years.
 
There never was any problem with customs or others about collecting, and
even the dive shops I used were not strongly against collecting in
moderation if you didn't harm the corals that are important to tourist
divers.
 
If you want documentation, you could copy the letter I got from Fsheries
Bureau in Fiji.  It is on the Internet HSN
  http://www.hits.net/~hsn
 
Aloha,
 
Wes