Google image search, when you use the right settings, is a great way to find free patterns for stained glass or any other craft.
The trick is to go into the advanced options. Choose "Line drawing" as the type and "Black and white" as the coloring.
After clicking on the thumbnail image, click on "Full-size image" on the right to ensure you get the most detailed version of the pattern.
To make this whole process even simpler, I setup a Free Pattern Search Engine. It takes care of setting type and color options and of fetching the most detailed version of the pattern. Then it's automatically uploaded to Rapid Resizer Online.
This service will let you crop the design, filter it to save money on printer ink, then precisely print it to any size. Enlargements over a few pages large require a subscription. Or you can then download the pattern and print it with any other program.