I hear these guys http://www.desser.com/ are a good source for aviation tires.
They have a big selection. Great Quality in my experience.
For new design it requires tooling. It's unlikely 200 - 300 tires is sufficient to cover the cost. You will probably be asked to pay the NRE and tooling costs. Estimate 50k - 100k as reasonable. Probably another 50k for TSO.