Here I go again answering my own query years later (this time with help). The maker is Rob Knottenbelt of Britannia Creek Glass in Wesburn, Victoria, as suggested by Ross. The JHS is a corporate logo, as I thought, and the Gilbert Oxford is a product of that company. These were made as corporate promotional gifts.
JHS is James Hardie Spicer, a division of the James Hardie conglomerate, best known in Australia as a major producer of products containing asbestos through the 1950s, 60s and 70s. The Spicer company was a maker of fancy paper products. Hardies had bought the paper-maker a few years before these paperweights were commissioned and rebranded the company a few years later (I wonder why?). Gilbert Oxford was a new paper product being marketed.
Thanks to Ross for extra help in tracking down Rob Knottenbelt to get confirmation from the source.
Trevor