I never had an issue getting parts from the USA. I used Troyer Performance (
http://www.troyerperformance.com ) and sourced a whole engine rebuild. By talking with Mike Troyer on the phone we arranged all I needed to upgrade the engine and I bought custom cams, a set of pistons and rods and valves etc and at a competitive price. The issue was finding someone who would talk to me and who understood the engine and what I wanted to do - which was basically to get the best of the motor for the application.
I also talked to a mate in Calgary in Canada and he bought bits for me and sent them over - they were cheap compared to Oz. S0 all it takes is some thought and time spent with Mr Google!!
(and of course - $$)
Cheers
Pete