Oh yes, Sicilian buttercups look very much like golden campines. I can’t tell them apart. I got mine at Meyer hatchery. Mareks vaccines take at least 2 weeks to protect, and provide immunity, so if there were a lot of chickens in your area, it might be more common there.
The link for RAL is for collecting blood at home while the chicken is alive to do a PCR test, which the best test. It costs $20 initially and they send the collection equipment, and tubes, and you send it back for the test. My friend said it cost $38 for the total from Colorado to Texas. Let us know if you do that since we are all learning here.