Who is the right type of person to create construction drawings for a home I've already designed?
Some of the things you mention don't require anything specific. Wall and foundation diagrams are boilerplate. The truss company will design the roof system to fit your design. Joist specs are fairly straight forward, and a salesperson at your local lumberyard may have the expertise you need. 

As has been mentioned, if you find the right company they'll be happy to work from what you've drawn. They may insist on re-drawing it, but there should be very little demand to change your design substantially. Keep looking for a smaller local outfit with a good reputation.