I agree with most of the posts on here. If a company doesn't offer an affiliate program there are 2 likely reasons why not.
1. The internet petrifies them and the only reason they have a website is they are conditioned to have one.
2. Managing an affiliate program is to time consuming for them and not worth the bother.
So how do you get round this
To set yourself as an affiliate network will cost big $$$$$$$$$$$$$
I am presuming that if you are approaching small businesses to market for them you are talking Paypal payment services type business. This could be managed by setting up an affiliate program for each company you offer to manage. Basically you would add the affiliate program to their existing website so they can offer an affiliate program and you just become an affiliate.
The more Im typing this, the more I think this could be quite a good idea!!!
You need an affiliate script to make the service I have found one here
PhpAffiliate :: Paypal Affiliate Software Script PHP
I have used it myself and it does offer a fully managed affiliate program.
So say for example you find a company that sells Handbags and uses a paypal shopping cart or buy it now buttons. You can upload the script to their website and then all they need to do is add an extra line of code to their paypal buttons. Then they have an affiliate scheme for their website. Im pretty sure you could charge quite a bit for this and as the code is only $34 US
Then you just join their affiliate program and post their links on your site.