A quick search produced 3 photos of T. Guant & Co shops.
The first one is from 1869 and is probably the one you have already referred to.
T. Gaunt 1869.jpg [ 157.86 KiB | Viewed 1971 times ]
The second photo shows the front of the Royal Arcade in around 1900 with the big clock face (in the left hand side of the photograph) next door to the London Stores.
T. Gaunt 1900.jpg [ 41.69 KiB | Viewed 1971 times ]
The third photo shows the front of the Royal Arcade in around 1910 with the big clock face (in the right hand side of the photograph).
Royal Arcade 1910.jpg [ 33.39 KiB | Viewed 1967 times ]
Also the Monash University Library in the Matheson Library Rare Books section has a 12 page Gaunt's rings catalog from T. Gaunt & Co. Pty. Ltd. Watchmakers, Jewellers, Opticians 337-339 Bourke Street, Melbourne dated 1940 which is available for public viewing if you want to go and have a look it may have a picture of the shop.