Hello
Shipping rates are calculated within our shipping classes. They can be statically called to get the details.
You can use this as per our commissions class. Read the source to find out how to populate the arguments. Details are in the get_shipping_due function in our pro commission class.
$rate = WCVendors_Pro_Shipping_Method::get_shipping_rate( $product_id, $vendor_id, $package, $settings );
cheers
Jamie.