What's the best way to create a connection between Salesforce and SQL server database where our business rules reside to determine contract price and accessories related to product selected?

I tried to create a validation rule for a field called "Jurisdiction" under opportunity product to validate against another field also called "Jurisdiction" under Account to see if Product Jurisdiction contains Account Jurisdiction.

A quick example below:
Account name AH Test is located in Nevada.
When trying to add product, for example, DARK SAMURAI which is not approved to sell in any Jurisdiction (N/A) to an opportunity under AH Test, show a message to account owner that DARK SAMURAI is not approved yet in Nevada. But still have the option for account owner to add to the opportunity.

Salesforce support told me this requires out-of-scope apex coding because it involves 3 objects: Account, Opportunity, Opportunity Product.

Any feedback is appreciated.