There are a large number of retailers from whom one can purchase a deck umbrella. These include Debenhams, John Lewis and House of Fraser amongst others.
Zack
buy one
Looking for Illy round table and umbrella
You can find the umbrella/parasol in buy mode in outdoor activities. You have to buy the umbrella, put it somewhere on the floor then quit the buy mode and you drag it into your sim's inventory. Whenever it rains and your sim has the umbrella in their inventory, they will use it every time it rains. If the umbrella is broken/your sim got hit by a lightning, he will get wet anyway.
An umbrella patio is an umbrella for your patio furniture. It typically goes in the middle of the table and screws in. It blocks the sun from you so you can enjoy your deck furniture.
Offer $500 dollars to buy a whole deck
At the 99cents store
target
You can buy a patio umbrella in Buffalo, New York at your local Home Depot. They have a great selection.
u can buy his structure deck in good games or eb games
You can try kokopelli.com or amazon.com
You can buy a phoenix patio umbrella at pricefalls.com. They have many umbrellas at very reasonable prcing. All prices are listed with their respected furniture.