First I'd like to point out the "sticky" thread Titled "where to find what you want" at the top of this forum. It is "sticky" because it is always on top and easy to find. "Where to find what you want has to do with pretty much every aspect of control line flying. engines, kits, balsa, hardware, flying lines and even ready to fly Cox planes and others.
Here is the direct link:
http://www.rcuniverse.com/forum/m_1133186/tm.htm

Please read through it and see!

As for engines if you act quickly there are Cox Sure Starts available at the time of this post from Cox. The latest news on the Cox can be found here:
http://www.rcuniverse.com/forum/m_7305584/tm.htm

You can buy new OK Cub engines here:
http://www.blackhawkmodels.com/hardware.html

The Brodak .049 and .061 can be found here:
http://www.brodak.com/shop.php?CategoryID=206

Virginia Hobbysport carries the OK Cub 049 and the Fox .049 plus lots of new parts for these:
http://www.virginiahobbysport.com/

Plus there are hundreds of engines on ebayevery week. Most mfgs, made these things in multiple thousands and there is no shortage in the used market.

Robert