Well, I'll be going off of this here:
http://swanamimi.deviantart.com/art/Utaune-Nami-concept-2-169305693?q=gallery%3Aswanamimi%2F24244391&qo=325
Shorts: Simple, buy some black shorts or something.
Jacket: Buy a white jacket, cut it to the correct length and sew the edge so it looks clean. Sew on some red fabric or something around the cuffs. For the black line going down the right sleeve, you could just sew down the side of it with black thread.
For the green...thing on the sleeve, get some neon green fabric, and sew it on. You can either try and embroider the yellow zig zag stuff onto the green beforehand, or use like...a yellow permanent marker or something and drawing it on?
Or, make your own jacket, and alter it.
http://mccallpattern.mccall.com/m6614-products-23007.php?page_id=118
Brown Belt: Get a stiffer, brown material and cut it out long enough so it sits on your waist and tilts down to your hips. Make a smaller loop and sew it around that for the little..loopy thing.
Red Belt Thing: Get a red and light red or pink...whatever color it is fabric and...here just read this... xD
http://www.ehow.com/how_8792973_make-vocaloid-belt.html
Shirt: It seems like it would be easiest to just make your own shirt. If you were to use this pattern:
http://mccallpattern.mccall.com/m4261-products-1839.php?page_id=118
I would cut the pattern in half for the main part, and cut it on a fold of the cloth. You'll have a seam going down your back, but you can put the zipper in on the front. Also add to the pattern before you cut everything to add in the turtle neck portion, make sure the measure your neck and figure everything out before cutting. Or use some scrap fabric and experiment till you get the desired look.
Legging Things: Find a pattern for long pants, or jeans or something...should be easy to find...or if you have some old black pants you don't mind cutting up, go for it. But it's pretty simple to figure out from there, add in some elastic in the red portion so it stays on your leg.
Shoes: Find some white shoes, something like these perhaps?
http://shop.ccs.com/product/model:124671/sku:11-01997/vans-classic-slip-on-mens/white/&SID=7284&inceptor=1&cm_mmc=SEM-_-Engine-_-Google-_-Plusbox
Use a red permanent marker and color the rubber part going around the shoe.
Headphones: Following something like this is helpful, just alter it to Nami's headphones and what not.
http://sailoranime.deviantart.com/art/Vocaloid-Headset-Tutorial-137249961
Sorry for the wall of text, but I hope it was helpful somehow, and if you need help or need me to clarify anything just ask. xD
