Some Australian bookshops stocking vintage Penguins (NSW & Victoria) part 1:

Lady Gail's Book Shop & Curios is a wonderful bookshop located in the small NSW town of Holbrook, about halfway between Sydney and Melbourne, and currently situated on the Hume Highway, although a bypass is presently under construction. For a secondhand book enthusiast it will be worth the brief deviation, however, for the house pictured above contains four rooms with walls completely lined with books for sale and it is open every day of the week. Many of the books she has (including Penguins) are priced at only $1.00 each. And Holbrook itself is worth a quick visit for anyone with young children, as the submarine which gives the town its name is a feature of the local park. I saw many other collectible novels at Lady Gail's, the type which other shops probably tend to reject or pulp, such as vintage copies of Pan and Fontana paperbacks. The stock of vintage Penguins is never particularly extensive, due to Gail's cheap prices, her very high-turnover, and my tendency to buy much that she gets in, but it is always interesting. My most recent purchase from Gail was a number of early Penguin Handbooks. 

And this is the wall of Penguins I found for sale at Mr Pickwick's Fine Old Books in Katoomba, with even more Penguins on the white bookcase in the foreground of the picture, and others in the discount bin at the front door. Most Penguins on the shelves were priced at $4.50 or $5.50; those in the discount bin were priced at $3.00. 

Katoomba seemed to be a town filled with bookshops and antique stores, and I found a few old Penguins in some of the other shops, although the best was the Salvos store on Waratah Street which had several selling at 50 cents each.

A search of Google Maps suggested that the town of Bowral was going to be filled with secondhand bookshops, but this proved not to be the case. There were only two and one of those was mostly devoted to hardbacks. However, the other was Bong-Bong Books, and it was certainly worth the detour off the Hume Highway, as they had loads of Penguins priced between $1.50 and $4.00. Apparently Bong-Bong Books is the bookshop featured in the video clip for Alex Lloyd's song Amazing (at 2.49). The owner directed us to the nearby Berkelouw Book Barn in Berrima, which was unfortunately closed for renovations, but I could see their warehoused stock which included a number of very old and well-preserved Penguins. 

And the Already Read Bookshop in Euroa helpfully keeps all their Penguins housed together, all priced at only $2.00 each