Can someone help me making a spread/moveset that will maximize a calm Milotic's defenses?
Right now, mine has 252 HP/240 Defense/4 Speed/4 Special Attack with Surf, Ice Beam, Toxic, and Recover...
How can I improve this spread without changing the nature?
I took the numbers from Team Ikki Tou Sen from the RMT archives, and a Calm Nature gives an extra four points in special defense, whole maintaining the same other stats... Is my new spread alright?
You are missing 8 more EVs. I'm not really sure how I should approach this question, so I will be giving you a comparison of the stats between Milotic from the Team Ikki Tousen and Milotic from your EV spread.
This is Ikki Tousen's Milotic.
Bold Nature (+Def,-Atk)
EVs: 252 HP/152 Def/4 SpA/96 SpD/4 Spe
Stats: 394 HP/140 Atk/255 Def/237 SpA/310SpD/199 Spe
This is your Milotic.
Calm Nature (+SpD,-Atk)
EVs: 252 HP/244 Def/4 SpA/8 Spe
Stats: 394 HP/140 Atk/255 Def/237 SpA/314 SpD/200 Spe
I gave your Milotic 8 speed EV so it can always outpace a max speed Adamant Aggron. I think your new spread is pretty okay. The team Ikki Tousen is really old though, but Milotic should be doing fine in the UU tier.
Edit: I'm not really sure whether you're planning to make your Milotic more of a physical wall, a special wall, or a balance between the two. The EV spread should really depend on what threat you are trying to make your Milotic capable of countering against. The 8 speed EVs should be a given though, since such a small investment lets it outspeed a max speed neutral Aggron.
Why not try and play around with Smogon's Damage Calculator?
http://www.smogon.com/calc/