Cake yeast?

Most natural food stores carry cake yeast in small quantities for home use. As mentioned, it has a short shelf life.

Giovanni, are you still in the DC area? The Kielbasa Factory on Rockville Pike carries it, but call before you go to be sure it is in stock. Vace on Connecticut Ave., in NW DC may have it as well. If you go to the Kielbasa Factory, be sure to get one or two of the numerous varieties of kielbasa that they carry and stop at Yekta, the Persian market, on the opposite side of the Pike.

Cake yeast is most commonly available to bakers as a bulk product due to its relatively short shelf-life compared to active dry yeast. In the US, cake yeast has been replaced by active dry yeast, but the product is very similar and yields identical results under proper handling conditions.

All commercial yeasts are is an inoculant of a yeast species (saccharomyces cerevisiae) that is responsible for fermentation of the final product. Different yeast products are therefore interchangeable with the help of a conversion table, such as this one: http://www.redstaryeast.com/lessons-yeast-baking/yeast-conversion-table