What would I search for to find bike hubs that attach on only one side like found on tadpole recumbent What is the name of the hubs used on recumbent tadpole trikes. Those tricycles that have two front wheels and a conventional rear wheel
They are often referred to as just that, a tadpole trike hub assuming you're looking for the front hub. They differ from standard trike hubs slightly. If you are in the united states or Canada you can get on of these from a shop. Let me know what country you are in as you are unregistered and I will do my best to answer.

http://www.jbi.bike/web/checking_product_description.php?part_number=38751