From what I heard, TY are hard to match into because everyone going into RAD, GAS, etc. wants it.
That's true. Open transitional year spots across the country were few and far between in this year's scramble, suggesting increased demand for these positions, precisely because they offer more variety and supposedly make you less of a peon than a prelim year in internal med. (Interestingly, prelim med spots were also relatively hard to get, though not so much as TY. By contrast, there were many, many surgical internships up for grabs - go figure.) But if you are a strong enough candidate to successfully match into rads, you probably have a decent chance at getting the TY you want.
As far as the categorical (PGY-1 to PGY-5) radiology programs with the integrated clinical year, they seem like a convenient option. Be advised that many standard advanced (PGY-2 to -5) rads residencies have symbiotic relationships with their IM depts, making it easy for you to slide into a prelim med year at the rads program you match to. I only know of a few categorical places, but check with auntminnie (or maybe scutwork.com) to learn more about particular programs you're interested in.