Search online for poems of Gustavo Adolfo Becquer, Gabriel Garcia Marquez and Jorge Luis Borges. All three poets are hugely popular and you are likely to find different compilations and anthologies including their work. Popular poets have been translated into English, so look for those names and then request the Spanish version.
Head to your local library. Even if your branch doesn’t carry a large selection of Spanish language poems, you may still be able to request books by inter-library loan. To find the best books, talk to your librarian but make sure you have a general idea in mind: a period, a specific author or a topic.
Visit the SpanishRomance.com website to access a variety of Spanish-language poems, stories and proverbs. While the website focuses on love poems, it also features a large variety of poems related to friendship, patriotism and community.
Search the SpanishInPeru.com website to find poems in a wide variety of topics and lengths. Because the website is aimed to English-speakers looking to learn Spanish, many of the poems have been translated or offer comments and notes for those with no full handle of the language.
Visit your local college and talk to the person in charge of the foreign language department. They should be able to point you in the right direction regarding choosing books and authors, or at least let you know if such books are available for loan to the general public from their library.