The Cobra only uses Feather Professional blades. The razor was designed specifically around this blade.
The only other blades on the market that are of the same length, and width are Kai Captain blades.
Kai blades are somewhat difficult to come by in the US, with 1-2 vendors stocking some of them, but not the entire range.
The Feather blades are generally around $22 for a 20 pack.
Do the Kai blades work in the Cobra?