If you want a club/mace that looks like a harlequin cane, go for it. You just can't also use it as a spellcasting focus, because there is no existing item that does that**, and creating one would be creating an item that's better than every other item of its type in the game. Why would anyone take a club or mace when they could take that thing instead?
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Pauper
**Edit: the closest thing to an exception to this is an item that isn't called out in rules, but is generally allowed by DMs (to the best of my knowledge, anyway) -- characters with a staff spellcasting focus should use those foci as improvised weapons in melee combat, but some DMs don't bother with that, mainly because wizards tend not to be optimized for melee combat anyway, so it's not seen as game-breaking to allow them to add their proficiency bonus and do a tiny bit of extra damage when they do decide to swing the staff for damage. Strictly speaking, though, a staff purchased as an arcane focus is "a specially constructed staff", not a quarterstaff.
Despite AL's insistence that DMs cannot make 'house rules', no prohibition on the house rule that allows wizards to use their staff foci as quarterstaves has been issued.