Bicycle cards are widely available in many European countries so the cards shouldn't look too strange. They are printed on Bicycle Maiden backed cards. Even in the United States, Bicycle Maiden Backed cards are rare. They are designed to look like Bicycle Rider backed cards with some subtle differences, and most audiences won't see the difference unless they are directly comparing the two back designs.
These cards are specially printed for this trick. You wouldn't easily be able to find gaffs in other back designs and it wouldn't be very easy to make your own.
If you are looking for a normal deck with the same back design take a look at these options:
Bicycle Maiden Back Playing Cards
https://www.penguinmagic.com/p/6779
Then here is a marked version of the same back design:
Marked Cards by Penguin Magic
https://www.penguinmagic.com/p/8474
