Good that you asked

It's really so often the case that the wrong things are advertised and even recommended by pet shops.
Tube and hood can be available at some pet stores, it always depends on what they have on stock. But these are rather common items.
Otherwise, it can be ordered from Amazon online, or from the website of PetSmart and other large pet store chains. I post here the links to the website from Zoomed directly so you can see it better:
This is the tube:
zoomed.com
The hood:
zoomed.com
Please check for the matching length (the hood is a tiny bit longer than the tube). The length should cover approx. 3/4 of the length of your dragon's tank. If you have a small tank and are still upgrading, I would recommend buying a slightly longer one, and use it diagonally until you have a longer tank. The 22 inch tube, 24 inch hood is a good choice.
The tube lasts one year and should be switched out then. After a year, the amount of UVB it produces decreases. Usually it won't get out suddenly, however.