I know of one and remember another........
Not sure of the name, but at the bottom of Avenida Colon across from El Bohen (sp?) , there is a place that does framing, mirrors etc. Its before the malecon and before the Brugal storage facility. I have had quite a few prints framed there and they did a good job. I also had a mirror made.
I also remember at one time a framing shop in the small plaza that has about 4 stores in it. It's on the corner near Supermercado Messon....... halfway between Caribe Tours and Supermercado Messon on the same side of the street as Messon.