Bonus missions:
Unlock the following numbers of bonus missions by entering the corresponding case-sensitive codes at "Main Menu" > "Access Additional Content" > "Promotional Content":

MISSIONS - CODE
Unlocks 4 bonus missions - 6aPHuswe
Unlocks 6 bonus missions - Cr34ufrE
Unlocks 6 bonus missions - 2Eprunef
Unlocks 6 bonus missions - JeM8SpaW
Unlocks 6 bonus missions - 2Tuw5esw
Unlocks 6 bonus missions - tr99pUkA

Promotional codes:
Go to "Main Menu" > "Access Additional Content" > "Promotional Content", and enter any of the following case-sensitive codes. Each one will unlock a bonus mission.

tr99pUkA
THaCupR4
tar3QuzU
SpujeN7x
sa7eSUPR
JeM8SpaW
Cr34ufrE
96CesuHu
2Eprunef
zUmU6Rup