About souvenir fridge magnets: I would like you to change this to more natural English please.
- - - - -
The magnets which this book described may be discontinued or sold out.
This book shows some useful URLs about the sightseeing places.
However, the magnets are not always sold at the places.
You shouldn’t ask about the magnets to the places because probably, the staff members at the places don’t know where to sell them or if they are on sale.
sembra naturale?

The english on this is actually really good!

But there are a few words I would change to make it flow better. I made them stand out by capitalizing them.

The magnets THAT this book described may be discontinued or sold out.
This book shows some useful URLs about the sightseeing places.
However, the magnets are not always sold at THESE places.
You shouldn’t ask about the magnets AT THESE places because probably, the staff members don’t know where to sell them or if they are EVEN on sale.
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So, when there is more than one place or thing you are talking about you would use "these" instead of "the".

For example:
"These kind of places are all over the globe!"
to get the point across that there are many i would use "these"

Also, one more thing. In
"You shouldn’t ask about the magnets to the places because probably, the staff members at the places don’t know where to sell them or if they are on sale"

I had deleted a few words to make it more natural.

Such as:
"at the places" near the end of the paragraph, only because it is extra information. Its not really needed.

I hope i helped, feel free to ask any questions. :)