I worked for a medium-size web agency who used a third-party marketing company. That marketing company cold-called companies on their database, kept track of things like when they last had their website rebuilt, what technology they used, the features, the name of the decision-maker or person responsible for procurement, etc.

I believe the marketing company were on retainer by a number of web agencies, and when they found a lead, they referred it to the most appropriate agency (for a percentage commission) - the agency then continued the sales process (e.g. with a pitch, an RFP response, etc).

I suspect there are a few reasons this model worked:

* The marketing company maintained their database over the long term, so they could discuss previous developments, plans the customer was making, etc.

* Providing leads to a number of web agencies (rather than each agency having a small in-house telemarketing team) gave the marketing company a greater economy of scale, which meant they could afford to invest in tools and training that were specific to telemarketing.

* Providing leads to a number of web agencies allowed the marketing company to generate revenue (commission) from a more diverse set of needs, e.g. sharepoint projects to one agency, wordpress projects to a different agency, etc. If a small agency were doing their own telemarketing, their conversion rate would generally be lower, because they would end up missing out on potentials leads, from not having a particular specialisation.

That remark was mostly meant to be understood as a joke, but since you asked:

Depending on what you're doing, you can Google businesses that need help, get their contact details, and go to town. See a business with a busted site? Check for their contact details, call them up or email them, try to get a response, convince them of why they need you to build them a better site.

Cold call.

Just find a local web design agency, for example, and send them an email introducing yourself and asking for work. There's plenty of resources about this, shouldn't be a huge mystery.