Is this popular to find in your everyday grocery store? I'm looking to do a quince, manchego cheese crostini but can't find this ingredient. I just learned of this combo recently so not too familiar with quince.
Quince is very seasonal. This time of year it's found in many supermarkets. Around here, for instance, Fresh Market, Meijer, and our local health food coop carry it. Presumably others do as well. I was going to get some for the same reason as you. But they're kind of expensive. My recipe for quince paste calls for 4 pounds of fruit, which would have cost me nearly 12 bucks. So I passed. Quince paste is available on-line from many suppliers, particularly those who either specialize in, or have a broad line of, Spanish products. A quick search should fix you up.
Thanks for the advice guys. Didn't realize it was so pricey? Looks delicious, especially paired with the manchego.
Quince are also available around now from farmers' markets. Yeah, they're pricey, but you can actually use the whole thing -- I took the skin and core and seeds and boiled them with water to make pectin. Membrillo is easily ordered from Spanish food Web sites, like La Tienda and Despaña. Since it's highly concentrated, a little cube is enough. And since it's a form of preserve, as long as you store it carefully, it will keep pretty well for a long time.