I think that the best company to approach is Lucas oil. They have their "On the edge" series on Speed.
I actually had the same thought w/ LUCAS 2 years ago, and did approach them. Got a really nice decline letter from them (which doesn't usually deter me from continuing to try in the future), but in the letter the listed the
$1,000's of dollars there already had budgeted on 'grass roots' racing programs all over the U.S. and also told me how far ahead they planned their budget...
I've got similar responses from a few other companies and see a trend in the 'timing' for some of them to get into their advertising budget...others seem to have a open budget (at least for smaller projects) all year round.
An interesting response I received once - from a big box store chain was to concentrate on local stores and not on the corporate level for smaller event type sponsorships.
...I must add, I don't really look for many, nor rely on many sponsorship deals for the series I promote/direct except for some small support to help keep the series alive every year - and for certain special events like our upcoming **ALLSTAR SHOOTOUT** which is a very small participation event for former and current 'Series Champions' from the first 6 years of our series.
This event has built some great support from with-in the R/C community and will have a payout of over $1000.00 in cash and prizes to the winners of this 2 segment event.