I’m trying to locate information on an easy to build throttle schematic for HO, something more recent than the December 77 article in the Model Railroader. Does anyone have anything available or info for where I can get this?
I’m not certain I understand the question. Are you just trying to build a stand alone electronic DC throttle, or do you mean a walk around throttle bus with train forwarding?
These have several…
http://home.cogeco.ca/~rpaisley4/Throttles.html
http://www.discovercircuits.com/M/model-trains3.htm
Just search for “schematic electronic throttle train” and there are many many hits.
See http://home.cogeco.ca/~rpaisley4/CircuitIndex.html
The older rheostat-based circuits of '50s and '60s do not work well for a mix of can and open frame motors because of the huge difference in current draws. Stay with a more modern transistor or IC-based controller circuit.
If you have to buy your parts at Radio Shack, it will probably cost more than buying a new Tech 4 from MRC. 
Check out the Cooler Crawler transistorized throttle system designed by Rich Weyand, Bill Pistello, and Bill Reid.
The construction article appeared in the February 1995 issue of Mainline Modeler magazine, and can now be downloaded from TracTronics, Incorporated. This site has the schematics, construction details, and information about kits that are available.
Look for the Cooler Crawler article. Although designed for use and tested on N-scale layouts, we use it on the Cochise & Western Model Railroad Club’s 20x40 foot HO scale layout and have had good results with it.