Australia had a relatively short golden age of comics, thanks to World War 2. The Australian government put in place restrictions on comics (and other publications) so that importation was banned, and reproduction of foreign comics (through syndicated proofs) also ceased. Australian-created comics came to the fore and, after WWII ended, many of the importation bans continued to preserve and foster the local comics industry. Some returned servicemen became comics creators. But the import bans were less stringently enforced, local reprints of American comics were comparatively profitable to locally produced comics, and the spread of television as mass entertainment combined to eventually kill off most of the Australian comics industry. And the direct importation of comics recommenced. (It's more compiicated than that, of course, but that's a simple overview.)
Many Australian comics took their lead from the displaced American comics. I can't tell you how many versions of, say, the Lone Ranger there were (Westerns were popular, as there's a degree of comparable experience between the American and Australian expansions across their landscapes), but there were also new ideas. Silver Flash, to use the example to hand, isn't a close imitation of an American comic, though the frogman/undersea genre is popular enough to be supported.
The creator of Silver Flash, Virgil Reilly, was a known comics creator, particularly as some of his illustrations included glamorous young girls, referred to as "Virgil girls", meant that he had an established audience. Reilly favoured nautical adventures for adventure stories, and he sold the concept of Silver Flash as a series. (The name may be derived from a popular science fiction comic strip, Silver Starr, which may have lead to some of the themes in Silver Flash.)
Because comics were seen as a disposable form of entertainment, there aren't a huge number of golden age Australian comics out there - some preserved by comics collectors, others recycled through the formerly thriving second hand books and magazines industry. Looking at some Australian comics groups on Facebook (and posts by active collectors), you'd probably expect to pay AUD $50-250, depending on condition - but you could get lucky on a private sale, or caught up in a bidding war that could blow out the price.
Info on Virgil Reilly on Wikipedia at
https://en.wikipedia.org/wiki/Virgil_Reilly. Also, searching for Silver Flash online means you often get results for Silver Age Flash, so prepare to be haunted by the Scarlet Speedster!