When I ran out of speed spheres the quickest way I found to rebuild my supply was to go to the monster arena. There I fought the Condor from Besaid over and over having Rikku mug it while she was wearing her Godhand. Doing this had several benefits:

1) Wearing the Godhand has the gillionaire ability and that paid for the fight.

2) Mugging it gave me lots and lots of free phoenix downs and a few smoke bombs.

3) Going to the Arena made sure that I was fighting a creature that gave out the exact sphere I needed.

4) Using fiends from earlier places gaurentees an overkill with mug causing the fiend to give up 2 spheres.

Anyway I hope this helps.......I am still looking for Fortune Spheres, if any of you have a clue please share it! Thanks! :bgl: