Reconfiguring Shipping Class Cost “N/A” to mean “Not shipping to location”

Hi,

I refer to the “Shipping Class Costs” in the WooCommerce plugin under Settings > Shipping > Shipping Zones > Add Shipping Zone > Add Shipping Method > Flat rate > Add Shipping Method > Edit (Flat Rate).

The “Shipping Class Costs” will appear when there are “Shipping Classes” defined. See the diagram below.

By default, all the shipping class costs for the shipping classes are “N/A”.

Currently, when a customer keys in an address within a defined shipping zone, if the “shipping class cost” for a particular “shipping class” is left as “N/A”, it doesn’t show any shipping cost during checkout, but would still allow the customer to proceed with payment.

Is it possible, with some custom coding, when a shipping class cost is “N/A”, the checkout page would inform the customer that “we do not currently ship to his/her destination” and disallow payment to proceed? If yes, how would one go about it?

Thanks! Any help would be appreciated.

P.S. In case you are wondering why we need to do the above…
Scenario: Say there are two shipping class “small” and “bulky”. The site ships products in shipping class “small” to a customer’s shipping address within a “shipping zone”, but do not ship “bulky” products. While the shipping class cost for “bulky” is left as “N/A”, customer could still proceed with payment, but we would prefer that he/she is not allowed to make payment and be told that we currently do not ship to his/her address for those “bulky” items.