OK I am very interested in this and have a few nice ones
20mm them make a yate loon fan that is awesome! http://www.frozencpu.com/products/7559/fan-455/Yate_Loon_120mm_x_20mm_Slim_Fan_-_Low_Speed_D12SL-12C.html
for 15mm http://www.amazon.com/gp/product/B00NOTVCUQ/ref=gno_cart_title_0?ie=UTF8&psc=1&smid=ATVPDKIKX0DER http://www.amazon.com/gp/product/B00G9WDYEC/ref=pd_luc_rh_sbs_02_04_t_img_lh?ie=UTF8&psc=1 http://www.amazon.com/gp/product/B00T9D680U/ref=pd_luc_rh_sbs_02_01_t_img_lh?ie=UTF8&psc=1 http://www.amazon.com/Scythe-Slip-Stream-120mm-SY1212SL12L/dp/B002CYPWTG
They also make 12 mm scythe fans but it is garbage. They have more choices Like this http://www.amazon.com/Gelid-Slim-12-PL-Silent/dp/B00CS102SE/ref=sr_1_10?s=electronics&ie=UTF8&qid=1431705790&sr=1-10&keywords=slim+120mm+fan (that one comes in red blue or white leds) http://www.newegg.com/Product/Product.aspx?Item=N82E16835705067 Aswell as that one but that last 2 are color themed and may not work with your build where the others are more monochrome or black the silver stone slim also comes in white blade blue body design.