Well, he might first search through old wizarding shops in Diagon Alley. There could be some ancient and forgotten stashes of rare materials. He could also ask Hagrid for help. Hagrid has a great knowledge of magical creatures and their habitats. Maybe there are some creature - related materials that could be used in the staff. For instance, the feathers of a phoenix or the horn of a unicorn (assuming it's done in an ethical and legal way in the context of the fanfic).
Harry could use his connections within the school. He could ask Professor Flitwick about any magical substances that could be used for a staff. Flitwick is an expert in charms and might know of some charm - enhanced materials. Also, Harry could consider using some of his own magical items as a base. For example, his Invisibility Cloak might have some fibers that could be incorporated into the staff, giving it the power of invisibility at times.
He would likely use Transfiguration magic. This would allow him to shape the raw materials into the form of a staff. He could also use Enchantment spells to give the staff special powers like the ability to repel dark magic or enhance his own spell - casting abilities.
Well, in most fanfictions, he might use a special kind of wood like elderwood which is often associated with magic in the Harry Potter universe. Maybe he also adds some magical items to it, like a phoenix feather for extra power.
Maybe he finds it in a hidden chamber at Hogwarts. There could be some ancient magic protecting it, but Harry, with his knack for getting into trouble and finding things, stumbles upon it.
The fanfic could start with the daughter of Merlin's staff being raised in a muggle family, unaware of her true identity. When she receives her Hogwarts letter, strange things start to happen. As she delves into the wizarding world, she begins to have visions related to Merlin's staff. She has to learn to control her powers, which are tied to the ancient magic of the staff. With the help of some wise professors and her newfound friends, she gradually uncovers the truth about her lineage and the great responsibility that comes with it.
Perhaps it's a time - traveling wizard from the future who knows that Harry will need this staff to save the wizarding world at a crucial point. The time - traveler realizes the importance of the staff in Harry's hands and decides to gift it to him. Another possibility is that it's a magical creature in disguise. This creature, having a deep connection to magic and prophecy, presents the staff to Harry as a means of fulfilling a greater purpose in the wizarding world.
Dumbledore might offer some guidance. He has vast knowledge and experience. He could tell Harry about the significance of different elements in a staff and how to combine them to make a truly powerful and unique magical tool.
It could be Dumbledore. Dumbledore is always full of surprises and he might give Harry the staff as a last - resort weapon to fight against Voldemort. He could have been secretly researching the staff and its powers and decided that Harry was the only one who could wield it properly.
The staff could make him more confident. If it has powerful magic, he would feel more capable of taking on difficult tasks. So, his character might shift from being a bit hesitant to more assertive.
He could use the staff to battle dark forces in a more unique way compared to his normal wand. The staff might have some ancient magic that helps him overcome powerful enemies. For example, it could have the power to nullify certain dark spells or even turn them back on the caster. This would give Harry an edge in his fight against Voldemort or other dark wizards. Also, the staff could be a key to unlocking secrets about his family or the history of Hogwarts that he didn't know before.
Some 'harry potter staff fanfic' might center around the staff during the time of the first wizarding war. How did they protect the students? What sacrifices did they make? For instance, a story could tell of how Professor Dumbledore coordinated with the other professors to keep the school safe while also being involved in the fight against Voldemort.