Q:

Is it possible to get similar feature to Warmage Edge without becoming a Warmage?

I am levelling up an sorcerer npc, that accompanies PCs. He focuses on the use of fire magic. 
I really enjoyed Warmage Edge class feature and I wonder, if there is some similar feature, that may be obtained by a feat or magic item, but would be charisma based and would affect more than "only warmage spells". I was hoping I could find something in Complete Arcane or Divine, but sadly there was nothing.

Warmage Edge (Ex): A warmage is specialized in dealing damage with his spells. Whenever a warmage casts a spell that deals hit point damage, he adds his Intelligence bonus (if any) to the amount of damage dealt. For instance, if a 1st-level warmage with 17 Intelligence casts magic missile, he deals
  1d4+1 points of damage normally, plus an extra 3 points of damage due to his Intelligence bonus. The bonus from the warmage edge special ability applies only to spells that he casts as a warmage, not to those he might have by virtue of levels in another class.
A single spell can never gain this extra damage more than once per casting. For instance, a fireball deals the extra damage to all creatures in the area it affects. However, if a 3rd-level warmage casts magic missile and produces two missiles, only one of them (of the warmage's choice) gains the extra damage, even if both missiles are directed at the same target. If a spell deals damage for more than 1 round, it deals this extra damage in each round.

3.0, 3.5, Dugeon Adventures and Dragon Magazines allowed.

A:

No, there is no existing pre-made effect that will accomplish both the granting of that class feature and switch the keyed stat.
However, there are rules for creating new content built into the game. As such, you can work with your DM and create exactly such an item. For example, there are items, feats, spells, and powers which DO grant access to a class feature (just not the one you want), and there are also methods of switching the keyed stats (usually via a feat). Therefore, find an in-game example of each: a warmage, an effect which grants a class feature (such as a Monk's belt), and an effect which switches the key stat (preferably an effect which specifically switches the key stat from the warmage primary stat to your desired stat) in the game world, and use the item creation rules and or spell/power research rules in conjunction with the example(s) as a template to craft/develop what you want.
Might be pricey, but then you also have the advantage of DM approval built into the process. Also, some people have issues with the Monk's Belt, considering it to be an unbalancing effect as it can be used to grant, among other things, a boost to AC beneficial for any WIS focused character. 
This also gives you a great excuse to go on a quest in your game to collect all the things (people in some cases) you'll need. 

