Pathfinder 2's Travel Guide set prices for multiple trade goods including ingots of different metals (iron, copper...). Is there an indication somewhere of how much bulk would each of those ingots take?
GM Estimates, Probably 1 Bulk
Ingots aren't given Bulk entries in the Travel Guide, so their Bulk would be estimated by the GM:
As a general rule, an item that weighs 5 to 10 pounds is 1 Bulk, an item weighing less than a few ounces is negligible, and anything in between is light. Particularly awkward or unwieldy items might have higher Bulk values. For example, a 10-foot pole isn’t heavy, but its length makes it difficult for you to move while you have one on your person, so its Bulk is 1. Items made for larger or smaller creatures have greater or lesser Bulk, as described in Items and Sizes.
There are a few ingot items from other books that have Bulk entries, the vast majority of which have a common 1 Bulk. Of particular note is the Core Rulebook's silver ingot with 1 Bulk and a value of 100 gp, matching the Travel Guide's silver ingot in value and suggesting that 1 Bulk is appropriate for at least that ingot.
Whether 1 Bulk is a good value for the rest of those ingots would be up to the GM.
There is no standard size for ingots
Even in the modern world. While there are typical sizes, these vary by metal and, within a metal, by the application they are being used for.
For example, steel ingots range in size from a few hundred grams to 500+ tons. Aluminium ingots for smelting are usually about 750-1200mm long, 100-150mm wide, and 50-100mm tall. Gold is more tightly limited; ingots for delivery must be between 11 and 13kg and be 99.5% pure. Of course, gold ingots for use in jewellery making are much, much smaller.
You need to decide how big the ingot is and then work out its bulk.