Some doctors have samples of medications in their offices, however these samples are usually only for a short time, usually 1-4 weeks of meds.
Also the samples that are in stock vary, and a doctor will likely not give you samples unless you are seen as a patient (paid visit).
Many pharmaceutical companies have patient assistance programs for those that are low income and/or uninsured. You can contact the pharmaceutical compnay that manufactures the medication you are taking and inquire about such programs, they will likely mail you an application, or have an on-line application.
Also there are many low cost or free clinics that provide medication if you qualify. Consult your local yellow pages or do a simple internet search to find such clinics.