One of the things I would avoid doing is using Google image search for your research. I bet you have already done just that. If you have, think about how many others have done the exact same thing. You should consider finding a tattoo artist that can do a custom piece for your new ink.
I would recommend that you check out tattoo galleries that have a membership fee so you can avoid a possible duplication of your artwork. A paid gallery site can offer much more than a free site. It gives you resources such as tattoo artists and tattoo enthusiasts as well as recommendations of quality local tattoo shops. It makes sense to have a current list of local tattoo artists that are known for their quality. You are about to take a big step in getting something very permanent. Make sure you get exactly what you want. I hope you find just the right piece of artwork for your tribal horse tattoo.