Yea, that's one that eluded me....as well as the 3 star (or whatever it was called) every hunter mission. I was NOT going through that final hunt mission again. Too annoying/rinse/repeat.
Though there IS a very easy way (if you managed to hold onto/acquire the missable items). Though I was even too lazy to do that.
Sen sen sen for big defense for whirlwind attack
syn syn syn when it is untouchable
sab sab sab when he comes out to poison him
rav rav rav then to stagger him / kill him until he goes to untouchable
It was easy....I just couldn't be bothered with attempting that 30-45 minute rinse cycle with a controller attached more than once in attempts to 5 star it.
Though for an easy way to get the item collector, here are some easy steps: (though i never did it....again, i iz t3h lazy)
1.) Transfer save file to to flash drive
2.) Go to computer and load up save editor
3.) Max munnies
4.) Buy manufacturing items
5.) Rinse repeat till you have enough crap to make everything.
PS. Feel free to write your guide. I'm sure it will help people do it legit.