For my daughter's Ukitake, we used McCalls 2940 for her captains jacket. Simply leave off the sleeves.
For the komamura's shoulders, I'd use padding (covered in a tan material) similar to shoulder pads (dense, shape-able, foam padding). And covered buttons in the same tan fabric.
I'm not too sure how you could do the helmet.
IKKiCON VIII, All-Con 2014, A-Kon 25
Kayle (IntoxicatedPeng) - Drocell Keinz (Kuroshitsuji), Yuki Onna (Nurarihyon no Mago), 8th Doctor (Doctor Who), Soul Eater Evans (Soul Eater), Lucy (Fairy Tail) - Also attending Gallifrey One 25
Mara - Lulu (FFX), adult Nel (Bleach), Hagoromo Gitsune (Nurarihyon no Mago) WITH Baby Moogle, Trystan
Me - Mary Poppins, The Woman (Doctor Who, The End of Time), Sibylline Sisterhood (Doctor Who)