Yes, Bunnings has springs to suit, although you may have to trim them to length required. I used Bunnings Springs on both my 12" and 16" GSO dobs. The springs are usually located in the section where the cabinet making gear is displayed, they are in little packs (white and yellow coloured from memory). I suggest you take one of your springs along to compare, you want one that will be stiffer than the stock GSO spring, but the right diameter for the job.
Century Springs I believe they are:
https://www.bunnings.com.au/century-...pring_p3971189
Maybe not exactly that one but they have heaps to choose from.