Hilton garden inn still showing some out of block rooms for downtown including doubles and suites in the $500ish range for those still looking.
What date range did you use? I'm not showing any
Aug 3 (Wed) through the 8th (Monday). Wouldn't surprise me if the hotels are now only offering rooms for longer stays now even out of block.
Hope that helps, i'm still looking for a inblock room myself but came across this while searching.
Source:
http://hiltongardeninn3.hilton.com/en/hotels/indiana/hilton-garden-inn-indianapolis-downtown-INDDHGI/index.html
Love to stay there, but not for $500-$600 a night.