After the change to chewing gum on a string, smithing a stone banjo is almost always the optimal solution for the stone mariachis. You only need a spare ten-leaf clover or big rock. The turn cost is 1 turn to convert the clover to a rock, plus another 1 turn smithing (unless you have access to Innabox, are able to cast Inigo's Incantation of Inspiration, or have some variation of the Loathing Legion jackhammer available.)
Should you need to backfarm an instrument (e.g. because you neglected to save a clover), here are the choices:
|Instrument||Zone||Monster||Drop rate||Number of monsters||Combat %|
|acoustic guitarrr||Belowdecks||grungy pirate||20%||5||100%|
|4-dimensional guitar||The Haunted Gallery||cubist bull||5%||3||80%|
|plastic guitar||The Valley Beyond The Orc Chasm||Lamz0r N00b||10%||8||100%|
|half-sized guitar||South of the Border||irate mariachi||19%||5||50%|
|out-of-tune biwa||The Haiku Dungeon||Knob Goblin poseur||10%||5||90%|
The massive sitar may be purchased during the war if you fight for the hippies, but at 50 dimes the cost is substantial.
If you are a Turtle Tamer you can tame a dueling turtle to make a dueling banjo. Note that this will also cost 1 turn to smith unless you can mitigate it by having access to Innabox or being able to cast Inigo's Incantation of Inspiration. Additionally, if you did not do this while unlocking The Road to the White Citadel or collecting the ingredients for the wet stew, it will cost you up to 4 or 7 turns to obtain the turtle, depending on whether or not you have a Garter of the Turtle Poacher.