You can find it in Route 129 but it is rare.
you can get feebas on route 119 very rare
In Pokemon Ruby it's on route 113 and it's very hard to find it is a rare Pokemon so it's really hard to find...
fuji yama shushi
In the weeds were you can find when you dive (rare)
Slackoth in ruby are rare Pokemon and u can find them in petal burg woods in the upper part.
you can find groudon, mew, mewtoo, rayquaza, kyogre...
fight to the sky tower for rayqazza find latios or latias
You can get three rare candies in Pokemon ruby sapphire and emerald
Route 119. They are moderately rare, though.
You can find a lightball on wild Pikachu, but it is very rare.
he is in th routs 124and126 but is a very rare Pokemon to catch