A1: There is no cheats for getting mana eggs

A2: To collect a lot of mana eggs you can go back and forth through the desert or through the verse relm levels, especially in the level heading towards surmania zero.

A3: Easy stone/bomb egg
This works if you unlocked the door in the Baccula Ruins-Sandy Path that lets you return easily. Starting from Baccularn Desern-North, go to sandy path and move forward until you are in the room with 3 jars, destroy those. Move to the stairs up and kill the monster, head further and you will find 7 jars, destroy those and most of the time you will get a bomb egg, stone egg, topaz ring, antidote, panacea, holy salve, healing herb, and white sulfur. It is random but you always get egg/s. Unlike other area the jars here return when you exit the ruins then return, there is also a rainbow orb/save outside so its easy. Just repeat until you get 9 of each and head back to town for fusion and selling of topaz ring.