As a kayaker come surfer I can tell you that you won't have any luck at a surf shop. The only kayak manufacturer to utilize surfboard plugs was Fluid for the Element with the 4Fin plug system.
As for the positioning, the reason the fins are placed closer to the center of the boat is because it is in line with your hips which creates the drive for carving, it would be even more useless at the back. Fins are at the back of surfboards because a surfer's back foot is responsible for drive and turning.
That said, I don't think fins have ever been effective on kayaks, given my experience with a Riot Turbo and a Fluid Element. I wouldn't waste too much energy in getting some, unless your OCD is seriously overriding