Ignave's may have just the button you are looking for − along with sewing and hobby supplies, party and wedding decorations, ribbons and laces.
It is a long, narrow and dark store that is always crowded. You have to take a number to be served.
Ask around about where to buy something along these lines and everyone will tell you to go to Ignave's. I didn't even see a sign outside, but everyone knows where Ignave's is located. It is about a block and a half north of Parque Central on San Isidro.
More photos below in the slide show: