we've just replaced our bearings and axle on the boat trailer.
the cheapest place i've found is www.spinnythings.com.au but you have to pay for postage.
they quoted me $56 for a 39mm 60' round gal axle plus ~$15-$20 for shipping..
We were hanging for a fish and ended up paying $110 for the same sort. just to give you an idea on pricing.
i'm not sure if it is required but we're going to add a tack weld on the axle to the spacer (between the leaf suspension and axle) just for some insurance.