There does exist several ways to buy bitcoin in Hong Kong. Major exchanges don't have restrictions for Hong Kong based users. I can mention CoinMama, binance... I remember reading that also Coinbase exchange provide services to Hong Kong.
What i want to say is that you can use other methods, not necesseraly face to face using cash. Some other exchanges also offer you the possibility to buy btc using gift cads.
Even bitcoin hasn't yet a legal status in Hong Kong, i have found a long list of available ATMs in Hong Kong:
PMQ, Garden Meow, 35 Aberdeen Street, HG01-HG05, G/F, Block B, Central
Shing Lee Shopping Arcade, Shop 19, 1/F, 6 Wing Kut Street, Central
Worktech, 23/F, Island Beverly, 1 Great George Street, Causeway Bay
VELA Hotel, 86 Morrison Hill Rd, Morrison Hill, Causeway Bay
108 Percival Street, Shop D1, G/F, 108-120 Percival Street, Causeway Bay
Tidebit, 7/F Sino Favour Centre, 1 On Yip Street, Chai Wan
City Garden, Shop 31, Maxibase, Block 1-3, 233 Electric Road, North Point
The Hive, 33-35 Hillier St, Sheung Wan
WeWork, G/F, 40-44 Bonham Strand, Sheung Wan
Genesis Block, U/G, 273 Hennessy Road, Wan Chai
Gala Club, G/F, 405-419 Lockhart Road, Wan Chai
Wah Hing Commercial Building, Room 2502, 25/F, Wah Hing Commercial Building, 283 Lockhart Road, Wan Chai
Source:
https://www.bitcoin.org.hk/buy-bitcoin-in-hong-kong/However, you can always find someone near to you by searching in local groups or peer to peer exchanges like localbitcoin/paxful .