sponsorship is a relationship. it's not about what a sponsor will do for you. it's about what you can do for each other. as a sponsored athlete, it's your job to actively promote the companies who sponsor you. you do that by using their products, talking about their company, referring others to them, and getting involved with them as well (ie sponsor rides and events, promotional events, etc).
for bike clubs, you'll have two types of sponsors: cash sponsors who donate cash and industry sponsors who donate product or services. and sometimes you'll have sponsors who combine the two.
cash sponsorship is typically generated because of a relationship between a club member and a specific company. if you have a team member who is in a position to make funding/sponsorship decisions, or to introduce you to the person in the company who can make those decisions, that's your open door.
bike industry sponsorship is typically generated by a sponsorship proposal. each company will have specific guidelines on their website. typically, industry sponsorship is decided early in the fall, so it might be too late at this point to generate industry sponsors.
as part of your proposal, you'll need to determine just what constitutes a sponsorship. lots of companies will give you a discount, but how is this adding value to your club? remember, the more sponsors you have, the "cheaper" the real estate. so decide if you want to have 10 sponsors @ $100 each or 1 sponsor @ $1,000.
also, keep in mind that you probably don't want to have competing sponsors. bike industry sponsors will ask for exclusivity (ie you can't have both CLIF and GU as sponsors). the same should be true for your cash sponsors (ie you wouldn't have two real estate agents).
sponsorship is about relationship. it might take years to generate a solid sponsorship. and it will take lots of attention to keep that relationship going. make sure to really think about your goals for sponsorship.
rambling.....