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Whether or not the Hexcrafter's Hex Magus class ability qualifies for the Extra Hex Feat is probably debatable (it's not the 'Hex Class Feature' the Feat needs as a prerequisite, but the Hexcrafter gains 'the benefits' of having a Hex... and qualifying for Feats could be considered a benefit) so it's probably worth checking with your GM on that one before you do anything else.
Other than that it's generally difficult to gain class features without a dip into the actual related class... but thanks to the Broad Study arcana a dip into a different spellcasting class isn't as terrible for a Magus as it might otherwise be. If you're set on playing Bladebound (instead of just spending a Feat on Craft Magic Arms and Armour) then maybe drop the Hexcrafter and just take a dip into Witch (assuming it's the Hexes part of Hexcrafter you're after)? You'll need to find some Witch archetype without a familiar (like 'Gravewalker'), of course, 'cos Bladebound uses the usual 'one familiar per customer' slot for the singing sword instead.