Make a save then find one of the below systems and start scanning (L2) while flying around in the galaxy map. Once it picks up a planet you put a probe down to the planet then just reload the save you made 10 times. Job done as it doesn't keep a count within the save file.
Here's the full breakdown if you're getting stuck finding one that I got the list from;
http://www.gamesradar.com/mass-effect-3-planet-scanning-guid...Aethon Cluster (9)
Apien Crest (5)
Arcturus Stream (3)
Argos Rho (6)
Athena Nebula (9)
Attican Beta (4)
Caleston Rift (3)
Crescent Nebula (4)
Exodus Cluster (7)
Gemini Sigma (4)
Hades Gamma (9)
Hades Nexus (7)
Hourglass Nebula (7)
Ismar Frontier (1)
Kite's Nest (9)
Krogan DMZ (3)
Minos Wasteland (2)
Nimbus Cluster (6)
Nubian Expanse (6)
Pylos Nebula (5)
The Shrike Abyssal (8)
Sigurd's Cradle (6)
Silean Nebula (11)
Valhallan Threshold (6)