Chipamp.com used to be "the place" to get chip amp boards. They have since gone out of business though, but Brian Bell (aka BrianGT) has provided Gerber files for the LM1875 and LM3886 amp boards as well as the excellent snubber PSU board designed for powering up to two LM3886. And I found the old LM1875 manual from when I helped him test it.