Quick - advice on tannins

I plan to brew perhaps late tonight or sometime tomorrow so I just thought I might get some quick advice on tannins. I was reading about English stock beer and want to make an approximation. It's going to end up ever so slightly sour - if all goes well. I want to make a really complex tasting beer. I have tasted sour brown ales with a tannic taste and it was appealing. What is the best way to add a slight tannin note? I'm not talking turbid mash, but just enough to notice it. I would really appreciate any thoughts, thanks!