geographic sorting in e-commerce

We are building a complex website that sells products that require a teledoc experience before purchase. We have a segment of our audience that is national that will need to be funneled through another site to complete their order, whereas the local audience will be able to purchase directly on the existing site.

My questions is WHERE and WHEN to sort them. Should we make the geographical bifurcation clear on the home page, or wait until the user begins the purchase process? What would cause the least amount of friction?