I know of vary few people that have ever had sponsorship that needed it. And of them most have been given a little by few.

If you are going to do this you need to get your name out. Ytube, blogs, books and the rest. And that is long befor you start asking for items and getting money is long bet.

You are a photographer now so you must have a few top of the line cameras and with all the gear and leses you have you will not need any more now. And how will you ridding on a bike get them anything someone flying on a plain and renting a car not get them? Many pros go on shoots with crates of gear, lenses, lights, booms, pods, computers and power to run it all.
I Do not think Canon or Nikon will want one of there $8,000 cameras and a few $5,000 lenes to ride on the back of a bike If there is a chanse of loss. And there is a good chance it will end up in a river and stop working or the vibration damaging the parts in them. I know I have a kit lese that has lost AF and maby VR. There not going to hand any thing to someone that will not wow them. Think more National Geographic less snap shot.

BMW may hand out a bike or two a year but most do not. once word gets around XYZ hands out bike for you ride around on there will be endless list of 20 and 30 somethings begging bikes. TT Dose sponser people but most people use the sickers they got in boxes to hid scraches.

Now your best bet is to find people that make items you need but are not from the big makers. Ask them for one inreturn for storys and pics of you using them for there adds. But you are going to need to show them you can do this as in show them a story of riding around the world (fake or not matters little) and how there say .... tent and sleaping bag was home for a year and how it felt like going home setting up the tent and how you felt safe and dry in it. (photoshop backgrounds to add punch to the adds/story)

You can also try and do "food network" deal with you flying and ridding around eating things that most people will not. It is getting old but this is a new twist on it who knows they may even pay you.

You best bet is to forgo the sponsors for most items drop tents and most other cammping items. Sleep where you can couchsrfing and cheap hotels this adds to the drama. Wright for travil and moto mags for money, pics to fill the up the pages. Ytube the trials of the trip and gain a following you can make a bit off the adds there and get help on the way and may even get people to sponsor you that way.

Good luck!