A transformer converts AC to AC. To get DC out of it, you need a rectifier of some sort. A bridge rectifier is most common in this case.
Transformers are wound for a specific voltage multiple/divisor. That is, one side of the transformer takes 230VAC and the output is 30VAC. You could also put it in reverse and put 30VAC in and get 230VAC out.
They come in almost any voltage-voltage ratio you can think of, and finding 230VAC to 30VAC shouldn't be hard at all.