My starting point to search for trials is usually https://clinicaltrials.gov/ but there are other good ones.

I often just check the websites of prominent institutions where I could realistically travel by car (on straight interstates with tolerable traffic) or easy, affordable non-stop flights. From Central Florida, the former are mainly Moffitt and Mayo, with the latter including Houston, Atlanta, Baltimore, NYC, and Boston.

My trial was at MD Anderson, requiring me to spend 5 weeks in Houston.

It's important to speak to a human at your target institution / trial location as soon as possible. They often ghost people who send emails or leave voicemail. It helps to be "in their system," which means you've actually seen an oncologist (at least for a one-time consultation or second opinion) at that site, so you'll have an advocate with inside connections willing to refer you to the actual research coordinators conducting the trial.