Are you looking for a contractor, or advice?
Also be sure to set up a solid NDA with whoever you work with so they don't just go and run off with your patentable idea themselves.
option 1 > buy solidworks premium, get it modeled up, do some motion simulations, do some static simulations
option 2 > hire someone to do this. hire a design consultant if you think you need someone to critique the design and offer improvements, hire an analysis consultant if you just need someone to validate the design (like taking it somewhere to be tested)