I have a hard time believing that neither Bicycle John's nor Gil's (your two local shops) don't have carbon paste. Even if they don't have it, there are tons of places on the internet that sell it. Or maybe this is a case of not wanting to wait any longer to put it together?

Having said that, you're probably OK with a carbon post in an aluminum frame since over-torquing a seatpost clamp has a much lower potential for frame damage on a non-carbon frame.