Since its first publication, many editions of the classic text have been published and some of them are usually available in most university libraries. Inexpensive second had copies are widely available, too. You may want to get the second edition with Ian Steward's foreword from 1990.
Excerpt from the preface of the first edition
"A great discovery solves a great problem, but there is a grain of discovery in the solution of any problem. Your problem may be modest, but if it challenges your curiosity and brings into play your inventive faculties, and if you solve it by your won mean, you may experience the tension and enjoy the triumph of discovery.
Thus, a teacher of mathematics has a great opportunity. If he fills his allotted time with drilling his students in routine operation he kills their interest, hampers their intellectual development, and misuses his opportunity. But if he challenges the curiosity of his students by setting them problems proportionate to their knowledge, and helps them to solve their problems with stimulating questions, he may give them a taste for, and some means of, independent thinking.
Also a student whose college curriculum includes some mathematics has a singular opportunity. This opportunity is lost, of course, if he regards mathematics as a subject in which he has to earn so and so much credit and which he should forget after the final examination as quickly as possible. The opportunity may be lost even if the student has some natural talent for mathematics because he, as everybody else, must discover his talents and tastes; he cannot know that he like raspberry pie if he has never tasted raspberry pie. […] Having tasted the pleasure in mathematics he will not forget it easily and then there is a good chance that mathematics will become something for him: a hobby, or a told of his profession, or his profession, or a great ambition."
G Pólya, Stanford University, August 1, 1944