Look up publications of these professors to get an idea of what the lab does. Showing that you bothered to read about what the lab does and that you're actually interested in their work will score you points. In an email, you can impress them by mentioning that you read their publications. There's no harm in sending a brief, polite email introducing yourself, casually mentioning that you've read their publications, and explaining what you can offer the lab and what the lab can offer you. Many professors who don't teach undergrads may be open to having an undergrad in the lab. It depends on the individual circumstances of the lab/PI.
Remember a "no" may not mean that you weren't qualified and they didn't like you. The lab may not have enough funding to pay you, or their postdocs are brand new and not in a position to mentor undergrads, or they already have 5 undergrads and don't want more, or the PI was just recruited to industry and the lab's closing down, etc. etc. Good luck!
