Talk to the mother of the cactuar you are looking for in order to get a clue of where they might be, even a simple phrase like "snow" or "beach" would help greatly, but some information can be misleading and confusing.
But in case you want to get it done and over with, here are their locations:
1.) Lobivia - Bikanel Desert, Oasis.
2.) Toumeya - Besaid Island, Beach.
3.) Lobeira - Leblanc's house, in a chest in Ormi's room.
4 & 5.) Areq and Arroja - Calm Lands, Bridge (on a chocobo before entering Mt. Gagazet).
6.) Islaya - Thunder Plains, North.
7.) Chiapa - Kilika Forest, climb tree overhanging river (press O near the tree).
8.) Erio - Mt. Gagazet, edge of cliff (where Seymour was fought in FFX).
9.) Bartschella - Kilika Island, inside Dona's House by the stairs.
10.) Frailea - Bikanel Island, after getting Bartschella, go back to the Cactuar Nation and go into the Cactuar Hollow, you'll find this little guy and fight Jumbo Cacutar. Be prepared.