For NT, you are limited to IB (since MF blew up) as far as I know. Otherwise, I think CS AES and Newedge are decent options.
You will have to contact them. https://www.credit-suisse.com/investment_banking/client_offering/en/retail_execution_services.jsp https://www.credit-suisse.com/investment_banking/client_offering/en/aes.jsp