Most malls have a NIKE shop which are the offical retailers.
As for the small shops.
Go to :
Long Fu Street,east district of Beijing,there are 2 shops aound which are the best 2 in BJ IMO.(I am not sure about the exact address,sorry) TMac1
Oriental Plaza -- New Oriental Shopping street Sports Zone, north-east entance of the street (said to be the biggest offical NIKE retail place in Asia)
TianYuan LiSheng -- Face to SunDongAn Square,specailzed in Sports Bands,Equipments,Gears etc.
SunDongAn -- North of WangFuJing Street.Sports Area at ground floor.
Sogo Mall -- XuanWu Men.Sports Area at 3rd floor.
Parkson Mall -- FuXing Men. Sports Area at 3rd Floor.
ZhongYou Mall -- XiDan Square. Sports Zone.
YanSha Friendship Shopping Center -- ChaoYang District. Sports Area.
SaiTe (forgot the English name thou) Shopping Center -- JianGuo Men ,Sports Area at 4th floor.
Quest? Sports shops -- Easy to find but not to promoted cuz they always do some dirty bizs behind the shelves.
Some other shops I've done biz with:
YaXin -- East of LongFu walking street OR North of DongSi cross.Next to KFC.Possiblly the best personal shoe shop in BJ.(Some NTer has been there and must have done some biz on the VIIs right? =)
AhHong -- I forgot the name of the shop but the owner's name. Inside of the LongFu walking street,or so called LongFu Square,face to McDonlad's
XinShuangHua -- West District, face to BaiTai Mosque
I've been asked for many times but no,I dont know where to get "cheap things",and as for other shops I've stepped in (I think I've visted most shops here),specailly those personal shops,they more or less selling something that should not be promoted at NikeTalk.So if you are looking for authentic stuff,do buy from others,no matter how real the shoes look,unless you are good enough to tell.
Hope this help and please correct me if I was wrong or missed anything.I will update for more if necessary. TMac1