Where can I find a second builder queue?

Check your items, there may be a second builder queue item there that will activate for 48 hours. The only other way is to reach VIP level 6 and that will permanently activate the second builder.

For more information on activating the second builder queue, please see this page o four guide: https://www.appgamer.com/rise-of-civilizations/strategy-guide/unlocking-the-2nd-builder-queue