Where should I start looking for these fares? The airlines in the USA and the US websites (where I am at present) are quoting very high fares. Thanks.

You don't mention when you want to travel, or to where in the USA. Time of year will likely have impact on price.

January - to LAX

Hi, Sue5250!

I find www.webjet.com.au quite helpful.... and there are also a couple of sites that will email you any great deals as they come up (about three weeks ago I heard of a $AUD299 one-way fare from Sydney to London, which is the cheapest I have ever seen it -- but you had to leave on one special day in November).The sites are are:
www.bestflights.com.au
www.travel.com.au.
Hope these are of use!

I've used travel.com.au, and found them good.

Travel in some of January is considered peak season!