Errand of Duty

Create a 1/1 white Knight creature token with banding. (Any creatures with banding, and up to one without, can attack in a band. Bands are blocked as a group. If any creatures with banding you control are blocking or being blocked by a creature, you divide that creature's combat damage, not its controller, among any of the creatures it's being blocked by or is blocking.)

Cooperation

Enchant creature
Enchanted creature has banding. (Any creatures with banding, and up to one without, can attack in a band. Bands are blocked as a group. If any creatures with banding a player controls are blocking or being blocked by a creature, that player divides that creature's combat damage, not its controller, among any of the creatures it's being blocked by or is blocking.)

Benalish Infantry

Banding (Any creatures with banding, and up to one without, can attack in a band. Bands are blocked as a group. If any creatures with banding you control are blocking or being blocked by a creature, you divide that creature's combat damage, not its controller, among any of the creatures it's being blocked by or is blocking.)

Chatzuk, Mighty Guitarist

Banding (Just ask around until you find someone who knows.)
Creature spells you cast with banding cost {2} less to cast.
Whenever two or more creatures you control attack in a band, each creature in that band gets +1/+1 until end of turn for each creature in that band.

Formation

Target creature gains banding until end of turn. (Any creatures with banding, and up to one without, can attack in a band. Bands are blocked as a group. If any creatures with banding a player controls are blocking or being blocked by a creature, that player divides that creature's combat damage, not its controller, among any of the creatures it's being blocked by or is blocking.)
Draw a card at the beginning of the next turn's upkeep.

Benalish Hero

Beast Walkers

{G}: This creature gains banding until end of turn. (Any creatures with banding, and up to one without, can attack in a band. Bands are blocked as a group. If any creatures with banding you control are blocking or being blocked by a creature, you divide that creature's combat damage, not its controller, among any of the creatures it's being blocked by or is blocking.)