Kobo has revived the buy $50, get a $10 bonus card, offer for the US July 4th. The offer expires July 6. However, kind of unusually, the offer doesn't show up at Kobo UK. Kobo usually has the gift card offer across multiple country stores, even if it's linked to a US holiday. I haven't checked the Kobo stores in Canada or any European countries. (Canada might have for Canada Day ???)
Also somewhat unusually, there isn't (or I can't find) a link to the T&Cs for the offer, but I am going to assume they are similar to previous iterations of the bonus card offer. It does say it's one per customer.
FWIW, I'm surprised to see the buy $50/get $10 offer pop up again for the 4th. In the past, my memory tells me that the buy $50/get $10 has been only at year-end and Mother's Day. And the "ratio" is more often $60/$10 or even $70/$10 (as it was a couple of weeks ago, in mid-June). Although, of course, my memory could be wrong - I haven't been paying precise attention to when the better ratio comes around.
Info is on the normal Kobo US gift card page:
https://www.kobo.com/us/en/EGiftingCustomization