While I haven't done it Michael, (travel overseas with rockets) I think you're okay to bring rockets, but not any motors at all. The rockets will definitely get some attention (or be missed completely by the screeners) and it would be to your benefit to have some documentation to help them understand what they are and what they're for. A few rocketry magazines, a NAR or TRA membership card, stuff like that.
Also, I'd be especially careful to clean up any residue from propellants or black powder as those might set off alarms and close the airport.
To get your motors here, make contact with a local and have them sponsor your launch activities. Ben Jarvis came over to BALLS one year and he did this.
I've never transported fireworks or explosives across the boarders so I don't know what the situation would be with rocket motors.
I had a friend try to take an arrow fletcher onto a plane and spent a 1/2 hour trying to explain (archery team meet). We got on with a brake booster from a 77 Dodge Monaco but that was pre 9/11. We did receive some grief on the return trip from Phoenix, but the nick-nacks had LEDs and switches in them. They might have issue with altimeters or other electronics packages. If you're just driving across a boarder, I wouldn't see any problem other than maybe propellant, you could call and ask first. Locals 'fascist's? I can walk into a McDonalds carrying a side arm,... can you?
Here's my suggestion. Email the club (and vendor's for) who's event you're planning on attending. Explain the situation and that you want to spend money to fly some big rockets. There are plento people that like to work with the big projects, but money keeps them from that by themselves. You could ship electroncis (even the rockets) to the hotel or maybe even a club member. There are people that attend big launches, but don't fly because of too few flights to justify the launch fee. Get the word out and maybe you can hook up. If so, then you wouldn't need the papers (non-yuck) if someone else has them.
I would only offer the suggestion that you bring rockets that have not previously flown. If a rocket with burned propellant residue gets picked up by an explosives sniffer the air transport security folks will have a major problem with it (and unfortunately, with you as the owner).
Don't laugh - a couple members of the US International Team ran into this in coming back from the last World Championships.
I just flew across Canada and checked in a 14"x14"x70" long box containing a carbon composite airframe with aluminum/carbon fins. You should have seen the eyes bug out on the security officer working X-ray at "oversize baggage"! "What is it?" he demanded? I described it as "a display model for our booth" - and he simply nodded his head, said "oh, okay" and passed it through. It really wasn't any more sinister than that, but would have stood out like a beacon on X-ray.
The relevance of this to international travel may be doubtful..