Small displacement two stroke glow engines haven't disappeared completely. While Cox and Norvel are no longer in production, you can still find engines below 0.10 cu in being offered.

AP Engines is still offering a .061 model and a .09 model, both are available from:

http://www.towerhobbies.com
http://www.hobbypeople.net

Thunder Tiger makes their GP-07 (actually about .067 displacement I'm told) and it's available from

http://www.towerhobbies.com
http://www.thundertiger4u.com
http://www.infinitehobbies.com
http://www.ehobbies.com

Enya Engine is making two or three different varieties of their widely praised Enya .09-IV which can be ordered from:

http://www.enya-engine.com
http://richmondrc.com

Model Engine Corporation of America (MECOA) is offering a Fuji branded 0.05 glow engine:

http://www.mecoa.com

While there are no longer any .010 or .020 sized engines currently distributed in North America, many small model enthusiasts are still building planes and trading for these tiny powerplants on auction sites and classified sections all over the Internet.