As far as getting "free" bikes, your best bet is to go through a dealership who can pull support from the manufacturers based on your accomplishments. Or a dealer that is willing to work with you on their own.
For example, DGY is probably Illinois' largest and highest volume motocross dealer, and they supply bikes to both pros and amateurs. For example, the Subway Coca-Cola Honda MX pro race team gets their bikes from Honda but via DGY Motorsports. Also, I know some woman MX racers who have done well at top events, like the Loretta Lynn Amateur MX National, and they will get a deal worked out with the manufacturer/dealer. Like where they will buy one Suzuki from DGY and get a practice bike for free via Suzuki support. I have also seen where the shop will work out special deals for big races, like sending the racer with a used "parts bike" so if they need anything, they have a whole bike at their disposal.
I also know of dealers who let racers "borrow" their bikes for the season. And at the end of the season, depending on the terms of the contract, either the rider will return the bike to the shop and the shop will sell the bike as used and absorb the one year depreciation loss or the rider will need to sell the bike as used and get an $XXXX dollar amount to the shop.
So there are options to explore if you're looking for bike help, but it usually starts with the dealer.
As for getting free product, the best way to approach that is to directly contact the manufacturer. Most industry companies have a rider support manager who can review your resume and presentation and they have a certain budget worked out for each year for free product and/or paying you to use their product. Usually these budgets are allocated out in the September-December time frame so right now might be a little late to get in the 2005 mix. I wouldn't expect much as for getting paid to use the products as some of the pro race teams may only receive $1000-$5000, if anything, from key sponsors. But some smaller industry companies who are trying to grow their business might offer paid incentives. For example, for each dealer that you can get to carry their product, they might pay you $100. Or each rider you refer to get their suspension work, they pay you $50. You would have a better chance of getting actual cash from outside sponsors like some local businesses or internet sites looking to get their name out there.
Another prime spot to approach potential sponsors is any national event you might compete in. For example, here in the states, the Loretta Lynn Amateur MX National is a great place to get support as many of the top manufacturers send a truck and support rep to the week long race for that reason - to get the top riders running their products. Or at Pro MX Nationals, again, the top companies who support the sport: tires, suspension, exhaust, goggles, filters, oils/lubricants, etc. are there and available to talk about rider support, especially if you can put in good results.
Good luck!!