the short answer to your question is "no, it is not hard to get a job in rad onc out of residency."
rad onc is a small field, each year there are only about 100+ residency graduates. jobs are typically posted on the rad onc specific websites, such as astro. it is probably just too low yield to post on broader sites that med oncs and surgeons use. many jobs are also never publicly advertised, and travel by word of mouth, or you just apply and if they are interested they will contact you. as residents, we also get mailings from rural hospitals advertising their openings.
of course, if you want that one cush private practice job in the middle of Manhattan or San Francisco, you will face competition. but i think it is easy to get a job overall, and the better ones are more competitive.