You can get them.
For Magnezone, you just need to level up Magneton to lvl.42
and for Mamoswine, it's still the normal evolution (Piloswine with Ancient Power).
The only ones you can't have for now are :
Regis, Deoxys, Rotom, Uxie, Mesprit, Azelf, Heatran, Cresselia, Phione, Manaphy and Darkrai