"getting" the Form 6NIA issued does NOT require either a hunting license, nor a match invite (despite what it says on the Form): provided you are a member of USPSA (perhaps being a member of IPSC is sufficient: I do not know). In my application, I include commentary that I am a USPSA member and require the Form 6NIA to attend multiple matches throughout the year.
However, for CROSSING THE BORDER, you WILL require a match invite (at least in the western half of Canada, this is the case). Right or wrong, these are the instructions the border guards are working under. I discussed this with one of them. As they were reviewing my documents (including the match invite), I commented that I had heard that the match invite was no longer required when crossing the border. The response was that their marching orders were that they are still required.
Therefore I never cross the border without one. My typical methodology is: if there isn't one immediately available from the match organizers: create one for them: email it to them: advise them that they're welcome to use it for others, but that I require one to cross the border. I have always had favorable responses to this.
-ivan-