Hi, Debra. Speaking for myself, I estimate 80% of my contractors are part of my immediate and extended networks. For the rest, I look to community colleges, specialty organizations, and search engines.
As to vendor evaluation, I ask to see samples. I work on ensuring the consultant has the right skills to address our performance gap. I pay careful attention to their intake process--are they digging to find root causes or are they trying to adapt our gap to their prepped programs? Are they looking to partner with us on our project or do they expect to drop in, deliver, and bug out? Judy Hale recommended some metrics for evaluating vendors in her book, Performance-Based Evaluation. While the book is due for a refresh, the content is solid (which you know it will be when Judy writes it). My CHRO also expects the vendor to provide references.