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Be aware though that just because they have previously been cleared by a clinic doesn't mean they are now and forever clear of STDs!
In my opinion (and experience) it is much safer medically and legally to go through clinic channels, unless you are very sure you can trust a stranger to get checked out to your satisfaction. It is more expensive to go through a clinic but I found the peace of mind to be worth the extra cost and more.
My clinic Queensland Fertility Group have a branch in Cairns, look them up in the Yellow Pages for more info. They can obtain donor sperm for you as well as handle the insemination procedures.