IA lists are often not allowed in any major or mainstream event/
GT/etc..
Among the major wargaming conventions out there, such as AdeptiCon,
NOVA, and WargamesCon, most have side or parallel events/tournaments that allow
IA units more liberally.
http://www.adepticon.org/
http://www.novaopen.com/
http://www.wargamescon.com/
for starters
You can also check out events like DaBoyz
GT, Feast of Blades, Bay Area Open, etc.; some or all may have some
IA allowable component to them. It varies, and I can't personally speak for anything aside from
NOVA.