There are numerous places to buy that type of chair you can try online, department stores, thrift stors, or even a garage sale. I guess it's all about what you want to spend on the chair and if there is a certain type that you are looking for
Target and walmart
buy one
locker, chair, towel, float, umbrella
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.
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.
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.
You would buy a folding chair if you need to have a chair that can be put away in a corner to save space. By being able to be folded, the chair does not take up as much room as a regular non-folding chair.
Ken needs to buy a new dining room chair, if two stores sell the same chair, he should look to buy the one at the lowest price.
Try this site www.patioshoppers.com A vast selection of lighted umbrella can be found here. other patio and umbrella accessories are also available here.