After a certain year IVI ammo was no longer sold to civilians. Ammo after that year isn't supposed to be in the hands of civilians. It's against military regulations to sell it or not turn it in so it could end up on the market through illicit means (theft, sold against regulations, etc.). It can of course end up in civilian hands through other means that aren't criminal but my guess would be the military wants to crack down on thefts from armouries by staff of questionable morals so they asked CGN to not allow it to be bought or sold by regular members. The military also sells the brass to private individuals for recycling but those who buy it are supposed to provide proof it was destroyed and not resold to reloaders.
I have a pile of IVI brass stamped as being made in the 2000's (I think the cut off date was 1992 or 1998 or something) but it was all range collected. The military sometimes shoots at the range I'm a member at and don't always police their brass properly. It's not illegal for me to have it but technically I shouldn't have been able to find it as the brass should have been collected and turned in by the soldiers who shot it.
If CGN, the largest online buy/sell/trade forum for firearms and ammunition in Canada, disallows the sale of IVI ammo or brass, those trying to sell it against military regulations or contract agreements loose a large portion of their customer base and hopefully deters them from violating said regulations or contracts.
At least that's what I've concluded from little bits of information here and there. I've been wrong before.