Tamarind pulp is available at Asian and Middle Eastern markets and specialty food shops.
Tamarind pulp is sold in a dense block that can be wrapped in plastic and refrigerated in an airtight container for up to a year. To reconstitute it, break off an inch or so of the block and submerge it in warm water for about 15 minutes. Press the softened pulp and liquid through a strainer over a bowl to separate the diluted pulp from the seeds and fibers. Don't confuse tamarind pulp with the less fresh-tasting tamarind concentrate that is sold pre-mixed in a jar.