You can find freelancers locally by committing a simple Google search, such as “Web Design Freelancers CITY”. Replace “CITY” for the name of your town, city or region.
You can also take advantage of freelancer platforms, such as Upwork or Elance. I would steer clear of outsourcing your project to 3rd world countries. The people might offer you an hourly rate of $5 to $15, however their work is rather task oriented and highly unstable. Very frequently they may also say “yes” to a certain task or project, although they don’t have the required skills. All of this may result into a massive amount of jQuery, uncommented code and quick hacks.
What I recommend instead is to find someone who is a native speaker of your language, check his portfolio and have a short interview / call.
A long term solution to this problem is to establish an active network with freelancers, each having their own specialty. Just as some agencies have a “careers” page on their site, you can add one for freelancers and list all of the requirements. In additon I recommend checking for local events on Find your people – Meetup and Eventbrite. This allows you to meet freelancers in person and also explore the possiblity of potential collaboration.
If you need external help more frequently, it may be helpful to either hire additional employees or partner with another agency. For example, if you primarily focus on web development, then you may want to partner up with a design agency. This way, you can offer clients either the full package or only development services. In addition, by having another agency as a partner, they would also focus on sharing projects, thus granting you an even larger client base. This is also a rather long term strategy, but can be highly rewarding, if you partner up with a good agency.