Actually if you are referring to Magnamon, he is an Armor Digivolution, so you need the Egg of Miracles, and he has to be at lvl 40 with at least 10,000 XP in Holy.
The best way for you to raise his Aptitude (which says 23 right now) is to Degenerate him down to Chibomon, then keep bouncing him back and forth between the two, or if you can, Digivolve him up to Veedramon or ExVeemon, then back down to Veemon. Once the Aptitude reaches 40, you'll be able to train him to that level.
As for where you can get the DigiEggs:
Courage : Pallette Amazon Friendship: Access Glacier Honesty: Loop Swamp - Chaos Area Kindness: Resister Jungle - Chaos Area Light: Sunken Tunnel - Chaos Area Love: 2nd Union (Story) Quest Reward Miracles: Login Mountain- Chaos Area Sincerity: Limit Valley - Chaos Area
I don't see why not. So long as you've finished the Union quest that was there at the beginning of the game(and you should have by now). So just go there, hop into that dark portal, and peek around. Don't worry about the Digimon there, they normally stick close to the norm of the area you came from (so long as the name at the bottom doesn't change, can think of a few times it's sent me to loop swamp)