pharmacies should not be refusing to fill a prescription, unless there is a doubt around the authenticity of the prescription (and the pharmacy probably has a procedure to report it). if it's possible to file some sort of complaint, that definitely should be done. the people at the pharmacy don't know more about your health than your doctor.
please don't. if it needs a prescription, probably there is a reason for it
In the US, the requirement for pharmacists to police prescriptions even goes as far as criminal liability for dispensing inappropriately prescribed controlled substances (see: “corresponding responsibility”).
Choosing to dispense, or not dispense ivermectin isn’t going to rise to that level, but no state Board of Pharmacy is going to take action against a pharmacist who judges that ivermectin is inappropriate for a COVID diagnosis.