Appropriate design patterns for this problem

I'm asking if anyone could help me in this problem

• Imagine an online shopping portal which displays the products for selling on its home page.
• These products are coming from a third-party vendor with which the portal has tied hands to sell products.
• The third-party vendor already has an inventory system in place which can give the list of products it is selling and their number in stock; there is no interface available to online shopping portal with which the portal can call the third-party vendor’s inventor code.
• We want to call the third-party vendor’s code which is incompatible with client (online shopping portal) code to show the products to users on the home page.
• Also, when online shopping portal users click on “notify me when item is back in stock” for a particular item that is out of stock currently, they get notified through email.

what design patterns should I use and for what?