Hey Sanguis,
That's actually intended behavior, it's supposed to be really tough to "suddenly" turn to magic studies.
Although I'm open to suggestions for balance tweaks. You can:
-check human town Trinket Shops for diamonds
-maybe there's a human shop that sells tools and might have a grimoire?
-raid dwarf fortresses for diamonds and/or grimoires
Of course, if your objective is to play as a wizard, that's another story entirely -
just start with a grimoire from Equipment -> Tools. My human adventurer from Save10 is carrying a Llama Wool Grimoire and a Sheep Wool Divine Focus, of all things...
Q: I'm going back and forth on giving the free "search for gems" reaction a chance to create a diamond, or adding a "search harder" option to get diamonds for those who are having the problem you are having.
Q: And for you Sanguis, in case you're really attached to your current adventurer, maybe you can try using the generic reactions... I'm not sure if they can adjust adventure mode on the fly, but it's worth a shot! (And I need to know that info anyway).
In the file reaction_modest_generic, in your SAVE folder not your raws folder, copy the following under [REACTION:GENERIC_3]
[NAME:Inscribe a Grimoire, Desparately]
[ADVENTURE_MODE_ENABLED]
[REAGENT:material:1:NONE:NO_SUBTYPE:NONE:NONE][BUILDMAT]
[PRODUCT:100:1:TOOL:ITEM_TOOL_BOOK_MAGIC:GET_MATERIAL_FROM_REAGENT:material:NONE]
[SKILL:ALCHEMY]
[DESCRIPTION:Inscribe a grimoire desparately by pouring your heart and soul into the act.]
[CATEGORY:EB_SPELLCRAFTS_ITEMS]
For fort mode, this can adjust reactions on the fly... I'm not sure if it works in adventure mode too.