I would suggest you stay away from the big "corporate" freight carriers - although they are extremely fast and efficient, you end up paying significantly for services that you probably don't need - ie. if you don't need it in 7 days, then it can and should go by sea freight.
You should be looking up companies that specialise in "freight forwarding", "freight brokers" and the like who deal with US to Australia shipping. These guys have all the linkages with different freight consolidators, etc in the US, can organise your crate to packed on in a container with other shipped products (ie. "LCL" or light container load) and then handle all the customs paperwork, quarantine and pick up or delivery once in Australia.
Anyway, DHL, FEDEX, and the like do all the "end to end" stuff but charge a premium because they control the whole logistics chain using mostly their own resources. OK if you want it in 3-7 days by air, but they will hardly be economical for a heavy pallet or crate.
So, I can recommend the following company that my friend uses for importing silicon, urethane and other plastics from the US - there are MANY others, so do your own research! - but this is a good place to start, my mate has had a lot of good experience. You don't mention which state but these guys "AMEROZ" are in Victoria but I am sure they can help out to any of the major ports.
Mr. Lee Hart
Phone: 1300 AMEROZ (if calling within Australia)
Phone: +61 3 9772 5768 (If calling outside Australia)
Fax: +61 3 8692 6274 Mobile: +61 407 877 047
http://www.ameroz.com.au/testimonials
All the best with it.