I would approach the local bank first and see what they say.
As someone else say, the truck vendor might be able to finance the operation
or give you some advice as to what financing options you have. They generally
get many requests like that.

I assume that you are seeking a loan to buy your own truck and let your wife
broker freight for you. That is a great idea. But, if all you need is a truck
and trailer - have you approched those that sell those items and see if they
will finance them?

If I am off base here let me know what it is you actually need to be a
independant contractor.

  Hi, Thanks for your question. SBA doesn't loan money directly to small business owners; instead, SBA can help facilitate a loan for you with a third party lender, guarantee a bond, or help you find venture capital. Here's what you need to know about SBA's role in the loan process. For additional information, check out what you need when considering applying for a loan, which includes details about credit factors that are taken into consideration as well as our Veteran-Owned Businesses page at http://www.sba.gov/content/veteran-service-disabled-veteran-owned. Good Luck!  

Depends on what types of service contract will you be planning. Have you
already visited your bank and took an advice from them?