Many Venus outlets stock them. Else, try Chinatown. Swanston, Ocean or small shops along the area. I used Hardhead for a while. Not bad, but i found a cheaper better alternative.
Imperial is a barber shop product, obviously would not be endorsed by saloons. There is a diff between a barber and a hairstylist / cosmetologist.
The only local retailers are PACT (@Orchard Central), KIN, TuckShop and Sundry and Hounds of Baskervilles (These are all around Haji-Kandahar-Bali area). The 1st 2 shops are men's speciality boutiques selling clothes, shoes and grooming stuff, the Tuckshop and Sundry is a hardcore denim boutique catering to rockabilly hobbyists, and Baskerville is an actual old school barber saloon staffed by a old ang moh barber. All sell Imperial @ $40.
tl;dr = imperial can buy locally but still cheaper to get online.