The US Army cancelled the XM-8 rifle program. So, chances are you won't see it in the USA. Unless, it's a custom modification of a SL-8 (there were some people trying to come up with this mod).
With so much interest (ie. actually military/LE contracts) in the HK-416 & HK-417, H&K has pretty much placed the XM-8 on the back burner.
Supposedly, they've renamed it the GVM-8 and were last seen demoing it to the Malaysian military earlier this year.
However, if it continues on it's present course, it'll probably be discontinued and share the same fate as the G-11K3.