[sarasi]

The reason you will sometimes see them written as du and di is as above- that's what you type to get ぢ and づ to come up on the computer. They are definitely not pronounced with a "d" sound though.

For the same reason you sometimes see "Sinjyuku" for Shinjuku and "Kitijyoji" for Kichijoji- it's an alternative way of romanising Japanese, but it's one that doesn't reflect the pronunciation well in my opinion.

My husband is Japanese, and his family name has a づ in it, but we always have to point that out to people when they write down the name as otherwise they would write ず.