Heavy Ball: Stow-On-Side Stadium from Ball Guy, or putting Black Apricorns in the Cram-O-Matic
Lure Ball: Hulbury Stadium from Ball Guy, or putting Blue Apricorns in the Cram-O-Matic
Friend Ball: Turffield Stadium from Ball Guy, or putting Green Apricorns in the Cram-O-Matic
Love Ball: Ballonlea Stadium from Ball Guy, or putting Pink Apricorns in the Cram-O-Matic
Level Ball: Hammerlocke Stadium from Ball Guy, or putting Red Apricorns in the Cram-O-Matic
Fast Ball: Rotom Rally, or putting White Apricorns in the Cram-O-Matic
Moon Ball: Circhester Stadium from Ball Guy, or putting Yellow Apricorns in the Cram-O-Matic
Note that putting the Apricorns in the Cram-O-Matic is not a guaranteed ball. Putting four of the same colour in gives you a 1% chance to get the corresponding ball. There were also several events for these balls, but they've ended by now.
Source: Cram-O-Matic, plus every single Bulbapedia Apriball page
Hope I helped!