The balusters were provided by the local stair company. But round metal balusters are available from most stair builders or on many sites like this: https://www.stairwarehouse.com/plain-round-iron-baluster-5-8/?setCurrencyId=1&sku=9701-SB-44&gad_source=1&gclid=CjwKCAiAivGuBhBEEiwAWiFmYaQwhR6bUZBL-VVPn0FyApwsLdQD15i30QRd0ldHe6qn6U4eoXeuxBoCL1kQAvD_BwE

And the vertical 2x2 square posts are actaully wood, and are just painted matte black to match the balusters.