I've had some success, but it's not something that you would expect to pay for a whole trip.
So far I've been given a couple of Camelbak hydration sytems, some tough Factory 909 handle bars and big dessert style hand guards and some aluminum sheet to make panniers from.
It's worth asking for 'luxury goods' from sponsors. E.g. I could survive without the stronger handle bars and the hand gaurds, but having them could make a big difference in the likely event of a spill. If you do it that way then you don't feel like a sponsors unwillingness to help will ruin your trip. You'll just have to cut back on the luxuries.
It's also worth contacting the distributors and asking for wholesale prices or end-of-line prices.
Trouble is many of the most expensive things you need to pay for in cash, eg immunisation, air tickets and bike shipping. Sponsors are far more likely to give you products than cash.
Make sure you get on very good first name terms with your local bike dealer (go to one of the smaller dealerships and deal with the owner) and tell them what you're planning. You'll be surprised at the discounts.
Break into the local club racing scene and help with flag marshalling or timing or editing the club magazine or something. Racing clubs are always looking for non racing members to help. That way people will recognise your face and recognise you as one of the good guys who hangs around the track doing all the shit jobs in the rain and mud. A lot of bike shop employees race and if you're marshalling or something they'll realise you are giving up your free time to support their hobby, so they might be more willing to help you and your hobby.
It's all about the personal relationships. It doesn't matter how impressive your trip is, if you're on first name terms with your suppliers they're likely to help out.
Before you approach someone for sponsorship make sure you have all the paperwork sorted and on hand, so if they ask you for any detail you can give them an immediate response. It's all about a professional image.
Remeber you never get something for nothing. It takes a lot of time and can be very disapointing when you get knocked back.
Thanks to:
SportsPro / Factory 909
www.sportspro.co.nz
Extreme gear / Camelbak
www.extremegear.co.nz
Ullrich Aluminium
www.ullrich-aluminium.co.nz
Ampro / MSR
www.ampro.co.nz