Costco gets the same molds as for Oticon. They are limited in some configurations being unable to be ordered. For example Ototherm is not available. You can get silicone (solid) or acrylic (solid, hollow), embedded (solid). Most configurations for canal and other locks should be available.
They take physical impressions. Inquire as to which staff member has the most experience with molds and consider having that person take the impressions and order the molds even if you swap back to the person you like for programming.
In theory one could get an Oticon mold elsewhere and take it to Costco for programming. Some Costco locations may be fussy about that.
Like anywhere molds sometimes need remaking. Some folks have hearing loss where figuring out the optimal mold design is not trivial.