Many of these are likely to be difficult to find. You might try looking on Amazon.
Macross II : Spacecraft and Deck Plans Volume 3
Sentinels: Complete Role-Playing Game
Robotech RPG Book 2 - RDF Manual
Robotech RPG Book 3 - Zentraedi
Robotech RPG Book 4 - Southern Cross
Robotech RPG book 5 - Invid Invasion
Robotech RPG book 6 - The return of the Masters
Robotech RPG Book 8 - Robotech Strike Force