Your question is a good one. The existing boons to boost sorcery do carry an additional penalty (flaw) as they are broad in scope of use. If you thought appropriate for your game you could allow an item that functioned as a tool of the trade for specific tasks such as "the bowl of Agragor" which provides a bonus die for divinations  or the "Black dagger of Zurin" that when used in blood sacrifice provides a bonus die when summoning demons. Of course sorcerors are greedy beings indeed and often covet items of power that others own. While not a full on Mcguffin it could still lead to some good story.

I do for the following reasons. In my games, tools of the trade "thief" applies to lock picking and mechanical traps, not stealth, climbing, or pocket picking. Favored weapon would not be sword but much more specific such as foil or rapier.

The examples I provided are not that limiting if you get creative. Think about the black dagger of Zurin that provides a bonus die when summoning demons...well you can summon a demon to do just about anything so that bonus die can really be applied to a wide array of end results.

Perhaps having the bonus die apply to if certain actions are taken. Such as the black dagger only providing a benefit with the "wounds"option and the bowl only with the "ritual" option.

In the end its just a way of controlling a very powerful game mechanic, which ultimately is limited by arcane power anyway. It boils down to how "high magic" you wish your setting to be.

Nevermind.   found it.  Thanks