Hi Don, You'd use the standard size, like this one: https://www.etundra.com/kitchen-supplies/coffee-tea-supplies/filters/bunn-20115-0000-filter-paper-for-12-cup-brewers/
The Bunn VPS Pourover Coffee Brewer w/ 3 Warmers uses a 7 1/4"" brew funnel (attached below). You will just need a standard filter that fits that brew funnel. https://www.etundra.com/restaurant-parts/beverage-equipment-parts/coffee-tea/brew-funnels/bunn-20583-0003-7-one-quarter-inch-brew-funnel/
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