Item: Octobass; requires two normal-sized bards working together to operate, but allows them to cast spells at the level of whichever is higher, with double the range and strength. Alternatively, a giant bard could play it like a fiddle, that would work too

Item: Monkbonce Dudelsack of Duplicitous Doxology: in the hands of a properly skilled Bard, it essentially allows the casting of a targeted Suggestion spell, except when targeted at a Cleric or other individual dedicated to a particular deity, they believe the Suggestion is coming directly from their deity, causing them to eliminate the spell’s limited duration and keep it in their mind as a holy directive.