Hi,

there is no "conventional" place to buy this lime
you can use regular type-s lime from home depot
you can find the video on how to prep it here:
http://youtube.com/frescoschool

however you really need a lime putty - you can buy it here:

http://www.FrescoShop.com
http://www.truefresco.com/frescoshop

also it will save you loads of time and anquish if you watch this DVD to learn about specifics of Fresco Plaster

http://www.truefresco.com/frescoshop/product_info.php?products_id=45