The orange will appear in Round 3 after 64 dots have been eaten. It may also appear later in the same round.
If you're selecting Round 3 from the start, remember that each dot is worth 10 points. You'll know that you're getting closer to the item appearing when your points get closer to hitting 640pts (assuming you've not eaten an energizer/power pellet or eaten a ghost at this point).
Eat it when it appears, and the achievement will pop.
Don't forget, you can set your lives to 5 in the settings before the game. You can also choose level select, where you can select any level that you have reached in a previous game.