All stages in dragon adventure have dragon balls hidden in buildings, rocks, trees, etc.
Each arena has 1 per battle. (all should have a ball, City (Ruins) always does for sure)
General Tao awards experience, zeni, and 2 purple items - fuse them to obtain him as a character.
I found the best way to use "Saiyan Saga" and choose "Hurry! Goku".
Then fight General Tao. (Southern Capital) Use Piccolo, have a lot of Health. When you fight Tao, don't try to kill him, knock him into buildings, trees, anything that breaks. Then you should find a dragon ball, if you don't, keep breaking stuff.
Having a lot of health helps because you will have to allow him to knock you around when you can't fight back (for risk of killing him)
If you have trouble knocking him into buildings, then use Piccolo's special beam cannon. Position yourself so there is a building between you, so Piccolo will shoot the building.
If you find a dragon ball, sometimes its hard to get over to it, knock Tao in that direction
Computer enemies don't care about dragon balls, but they may accidentally touch it, and they will get it, so get the ball as soon as possible.