In case you're interested, good demand scanners include
MBAM, Superantispyware, DrWeb's Cureit (not up-datable, re-download the .exe when needed) to name a few. (Some others= Spybot, Asquared, AVZ4, WinClam...apart from Clam, they are antimalware rather than antivirus scanners, but there is a lot of function overlap, these days.)
I've read about various means used to have two AV's designed to be resident forced into passive (demand) behaviour..some users appear to have success with Avira in this regard, by not installing the guard. It's a workaround, though, and not guaranteed.
AFAIK the larger demand is for users wanting resident protection, rather than the demand scanner market, which appears fairly well served.