We can add gift certificates in SCA webstore using extension Gift Certificate Groups.
This extension lets you display related gift certificates together on the Product Listing Page (PLP) and Product Detail Pages (PDP) of your site. Create gift group for different gift certificates. On the PLP, one gift certificate displays using the group name. When users click on a category of gift certificates, the PDP shows one gift certificate with all gift certificates in that group as item options for sale.