Many sites, including CoH Warcry host maps that allow you to locate the Enhancement Stores quickly. However, I think mine is the only one to include pictures, so you know what you are looking for. :D Seriously, there is even the location of the stores marked on the map that comes with the game, but I still had enough trouble finding them that I decided I wanted a quick reminder that can take me back to them. Also, I decided to group them by origin instead of just listing all the stores in the same Zone.
To view the maps, just click on the links below, or to the left. Each page also includes an image of the signs associated with each store, plus a picture of the building from the air to help you recognize it. (The building is always the same for each origin, even though the names are different) Note that all level 15-20 stores are in Steel Canyon or Skyway City, and all level 25-30 stores are in Talos Island or Independence Port. I don't include the 35-40 stores since I haven't gotten to that level yet. (It's my understanding you have to go on a mission to get access to them)
If you are having trouble remembering which Dual Origin Stores sell Enhancements for your Origin, just look at the list below. The stores that carry your Dual Origin Enhancements will be ABOVE and BELOW your Origin Store. (Wrapping around from Science to Technology at the top and bottom of the list) It may help to think of the Origins as a big circle, or a five pointed star, with the dual origins in between each of the "points" of the star.
Stores: Freedom Corps
Levels: 5-10, 15-20, 25-30
Dual Origin: All (in Level 25-30 stores only)
Stores: Orion Labs, Deimos Innovations
Levels: Orion Labs (15-20), Deimos Innovations (25-30)
Dual Origin: Genetic Alteration, Invention (Mutant, Technology)
Single Origin: Experiment (25-30 only)
Stores: Subgenetics, BiotechniX
Levels: Subgenetics (15-20), BiotechniX (25-30)
Dual Origin: Focusing Device, Genetic Alteration (Magic, Science)
Single Origin: Secondary Mutation (25-30 only)
Stores: Pandora's Box, Tabitha Fabish
Levels: Pandora's Box (15-20), Tabitha Fabish (25-30)
Dual Origin: Relic, Focusing Device (Natural, Mutant)
Single Origin: Extradimensional Entity (25-30 only)
Stores: Image, Inc., Future Dynamics
Levels: Image, Inc. (15-20), Future Dynamics (25-30)
Dual Origin: Gadget, Relic (Technology, Magic)
Single Origin: Technique (25-30 only)
Stores: Cooke's Electronics, Exarch Industries
Levels: Cooke's Electronics (15-20), Exarch Industries (25-30)
Dual Origin: Invention, Gadget (Science, Natural)
Single Origin: Cybernetics (25-30 only)