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Natural Latex will be a more expensive material for you to make seat cushions from (polyurethane foam is what most people use), but if you are looking to take advantage of its hypo-allergenic properties to reduce the presence of mold and allergens in the household it will work great.
Visit www.foamsource.com, they ship all of their custom seat cushions for free and you can build and order custom cushions online through the their custom cushion interface (http://www.foamsource.com/getcat.php/92). However, this interface works mostly with polyurethane foam which is the standard seat cushion foam. I think to get natural latex cushions you'll have to speak to a representative by calling in (the number is on the website). Again, you can't beat the free shipping particularly since you're in the NYC area.
Thanks and let me know if you have any further questions!