Retailers that sell many different gift cards?

neuen

Hello,

I hope you're all well. 

I'm looking for retailers, both offline and online, which sell a lot of different gift cards. The retailer must NOT specialise in gift cards (e. g. NOT like highstreetvouchers.com). 
AFAIK, most retailers usually only sell their own gift cards online or no gift cards at all - even if they sell gift cards in their offline stores. Please, let me know if you know anyone who acts differently. 
As for the offline stores, I know Tesco, Sainsbury's, Boots (different cards in different stores), Argos sell many different gift cards in-store. Have you seen any other retailers that do so? 
I'm particularly interested in Selfridges gift cards sold this way however I would also be grateful for info about other gift cards. 

Please, share your knowledge. Thank you!