Switching from tiller controls ? WTB parts

My fishing buddy has a 1975 (?) 25 hp johnson. Where can we find the stuff to make this a control box shift. He has the helm with steering and cable, needs the steering bracked and control box with cables. Any help is appreciated. He says it is a 50 yr anniversary motor if that helps anyone on the year. Thank you

See a dealer, they should be able to order the parts for you, you will need a model number.