"Since Iran, as far as I know, is still trying to get its first nuclear reactor going, I'm not sure where they'd get spent nuclear rods. Such rods would be in far greater demand in weapons research than for making dirty bombs."

It might be bullshit. But as for spent rods:

"Iran's current nuclear programme consists of several research sites, a uranium mine, a nuclear reactor, and uranium processing facilities that include a uranium enrichment plant. The Iranian government asserts that the programme's only goal is to develop the capacity for peaceful nuclear power generation, and plans to generate 6000MW of electricity with nuclear power plants by 2010.[1] As of 2006 nuclear power does not contribute to the Iranian energy grid."
and
"In 1959 the Tehran Nuclear Research Center (TNRC) was established, run by the Atomic Energy Organization of Iran (AEOI). The TNRC was equipped with a U.S.-supplied 5-megawatt nuclear research reactor, operational from 1967 and fuelled with highly enriched uranium.[2] Iran signed the Nuclear Non-Proliferation Treaty (NPT) in 1968 and ratified it in 1970. With the establishment of Iran's atomic agency and the NPT in place, plans were drawn by the Shah Mohammad Pahlavi to construct up to 23 nuclear power stations across the country together with the USA by the year 2000."
http://en.wikipedia.org/wiki/Iran's_nuclear_program

I don't think Iran has shortage of spent fuel rods. But safely doing anything with them is not as likely.