Worse place to try and get drugs in ibiza is in the clubs, probally sounds wierd but its a mistake everyone makes thinking its the best place, so easy to get ripped off plus a large chance most of the people in there actually bought the stuff before they went in and no one is selling. Just walk about in the day and ask all the ticket sellers you see on the beach etc they will sort it, Ive been ibiza 5 days and have always been sorted within a few hours of landing, once youve got a source like a ticket seller theyll be your "new friend" for the holiday, or just walk down the west end strip and ask the people trying to get you into the bars.
Its easy to lose it in ibiza though nights out turn into 3 day benders and whatever, believe it or not oscthebooklad a lot of people go to ibiza for the music and drugs, you can get ladies any time of the year, though they are a plus its not exactly what I go hunting for when out there