It looks like many crownstore methods are private, so I'd say your best chance is to use
Lua Code:
SHARED_FURNITURE:GetMarketProductCategoryTreeData():GetNumEntriesRecursive(function(entry)
-- do something with the entry
end)
I have only tried GetPlaceableFurnitureCategoryTreeData so far, but if it works similar it should give you all entries in the crown store. Just make sure that the "filter by" box is empty, otherwise it won't show everything.