does anyone know where I can get a 轰炸机 夹克 like Americas?????

Hmm lets see... Expensive way:Ebay 或者 something like that. Hard way: Attempt to make it 或者 find someone to make it for you.. 或者 the Easy way! 哈哈 Find a cheap jacked that looks close to it and duct tape the 50 to the back of it! I was close to doing that myself XD Its cool that 你 have the rest of the outfit :P (not the best answer but its some choices)

If your actually buying the cosplay outfit itself, try ebay, 或者 亚马逊 (I haven't check amazon, but i'm obsessed with amazon. it has almost everything...)
But 你 may find this shocking, but 你 can actually find a bombers 夹克 like Alfred's at the mall. try checking the stores. But really, my friend dressed up as Alfred with searching handpicked items, she got a bomberjacket at the mall, went to a fabric store, got the number 50, got a star, and a airplane, amde out of patches, put them on. And it came below 25 dollars.

I saw some on Ebay.

cosplays aren't always that comfortable though online...I'd say it's better to find a 轰炸机 夹克 style 夹克 at clothes stores and add the 50 on the back, the 星, 星级 on the left front side and the airplane on the left shoulder/sleeve... I helped my friend with her America 夹克 (her sister helped as well). it looks quite amazing!