Call of Duty 4 Modern Warfare
This gives you two options for the MP5.
A skin For The MP5 And Also Does The MP5-SD for COD4.
A Call Of Duty 4 Realistic MP5.
MP5 Weapon Skin with SD Black version 1.0.
Mp5 w.SD with Olive Weapon skin version 1.0.
Here's a cool reskin of the MP5 in CoD4 by Notsafeforwork that aims at giving you a more realistic look.