Not truly fresh calamansi as requested, but the likely best alternative. I, for one, am extremely happy to have found it! You can find these packages of 12 individually sealed pouches of juice for a measly $3 and it is found at most Filipino stores. It's a product of the Philippines and is 100% calamansi juice... no sugar, no preservatives, no added anything! A product like this is so very hard to find these days. I picked up this package at 3 R's on Montrose.
3 R's Filipino Grocery
2712 W Montrose Ave Chicago, IL 60618
(773) 478-2599

Part of the secret of a success in life is to eat what you like and let the food fight it out inside.
-Mark Twain