You really might want to consider farming this, at least at lower levels. On fairy right now, one fully charged belt will go for 250k, assuming you quiver the bullets. Definitely worth ~10 levels in Sarutabaruta.
On my old account i got this first try from a brown chest. On my new account im trying to get it and im 0/250+, If you want it nows the time with "Mystery Boxes Bastok" moogle enhancement.
But all in all, these numbers just go to show that everything in ffxi is pure luck, dont stress out over minor things.
The best advice I can give for getting this is take a Lv. 8-10~ job get the 5th page in book. And go to where Leaping Lizzie pops. Seems to drop often from Lizards Good Luck!
I took Grimjow's advice (see earlier in this thread) and go the belt on third or fourth casket while killing lizards in the Leaping Lizzie pop area of S Gusta. No leaping Lizzie, sadly, but this belt is now worth three times the price of her boots. :)