They do as Heritage and just about every organization does, advertise after someone has shown interest. Just write back on their mail-in coupon once or twice to get removed from the mailing list.
As far as your claim that Hillsdale is rolling in money, they are using their budget to avoid government funding and interference in what they teach, which is conservative American history and governance; they are providing scholarships for new students of government, the constitution and conservative thought; they have recently opened a graduate school of government in Washington DC where conservative speakers and thinkers can be readily available to our "overlords"; and as noted, they offer many publications and courses for free.
Yet you bitch about receiving an advertising circular. Okay.
I was a big backer of Hillsdale for decades until something happened between us and the curtain was lifted.
Our problem is not remedied by the patriot with a price tag organizations. We, the citizens, must get our local school boards to teach constitutional government. NO school is going to welcome another school into their campus.
I do recommend your reading about the founders on your own. It can be done.