"Heavy Duty Clutch" unfortunately is a very broad term. The clutch in it could be anything from a button, solid centre, single organic, twin plate, triple plate, carbon fibre, well you see my point. Every clutch has a different feel to it and also has a different feel to it when it is new/cold/worn in etc. So obviously without knowing what clutch was in it and your lack of experience with aftermarket clutches, you can't really blame the clutch. For example my clutch is an absolute pleasure to drive, however you may stall it every time you drove it and think it was a rubbish clutch because you are not used to it. See my point?
As to importing one, you would be silly to do that (not to mention this country doesn't need more R33's being imported lol). There is that many available to choose from it is a buyers market. Most people can't sell Skylines for months and months so you are in a perfect oppurtunity. Not to mention you can look at the car, test drive it, get it checked out which with importing you really can't do.