Here are Melbourne / Australia-focused UGC creator platforms and marketplaces that have large local creator databases (short notes + cited source for each):

• 99designs — large Melbourne-founded creative marketplace for design creators (global community of 100k–150k+ designers; Melbourne operations). (99designs.com.au)
• Influee — Australia-focused UGC platform that advertises thousands of vetted AU creators (site shows ~2,100+ creators in Australia and 80,000+ creator profiles globally/applicants). Good for short-form UGC video at scale. (influee.co)
• Theory Crew (Melbourne agency) — social / UGC agency that says it maintains a 10,000+ Australian influencers & content creators database for brand campaigns. Good if you want an agency-managed approach with local talent. (theorycrew.com.au)
• Creator Flow (Roar Global / Australia UGC marketplace) — rapidly growing AU UGC marketplace (public reporting of several hundred+ vetted Australian creators; runs creator meetups in Melbourne). Useful for brand-grade UGC video production. (roar.global)
• Insense — global creator marketplace with a large vetted marketplace (platform states 60k–70k+ creators and supports Australia as a market). Good for programmatic creator sourcing across many niches. (insense.pro)
• UGC Launch / UGC Database — UGC-specific database/marketplace advertising hundreds of verified creator profiles and advanced filters (positioned for fast direct brand–creator outreach). (ugclaunch.com)
• Roamni — Melbourne-based UGC audio storytelling/tour marketplace (local hosts upload paid/free audio tours and stories). Good if your UGC need is audio/location-based. (en.wikipedia.org)

Quick guidance

• For large-scale short-form video UGC across Australia (including Melbourne): Influee, Creator Flow and Insense are the fastest scale options. (influee.co)
• For creative design assets from a very large global pool of creators with Melbourne roots: 99designs. (99designs.com.au)
• For locally managed, Melbourne-centric campaigns with curated talent: Theory Crew or a local UGC agency. (theorycrew.com.au)

If you want, I can (choose one): 1) pull current creator counts and pricing for any 2–3 of these platforms, or 2) shortlist platforms best suited to a specific UGC brief (format, budget, turnaround, audience).