When you're through, you can search for "tubular skylight" and press search. You'll get over 500 hits that talk about this. Just go from there. If you want to narrow your search, read about 'Advanced' searches. This will help you decrease the number of 'junk hits' if you want a smaller list.
For me to tell you where to buy them would be fruitless. Your tastes and style and needs are not the same as mine. Besides, other than ordering and paying for these items, I've done the work. My best to ya and hope this helps.
PS: When you do the search use the double-quotes. It's part of the search-string. Also, if you subscribe to any handyman or home magazines, look in the ads in the back and throughout the magazine for these products. I've seen them a lot.