Sweetbreads are one of my favorite bits of offal, along with liver and tongue. In browsing through the postings, particularly on places in Testaccio, notably Checchino dal 1887, such dishes seem uncommon. Tripe gets a mention along with pagliata (calf intestine), but the other offal is absent. Given the historic meat-packing character of Testaccio this absence seems surprising.
Are there any Roman restos that specialize in sweetbreads?