What is this part and where do I find it? U58/406

It is a very small electronic part perhaps 3.5mm X 3.0 mm with 3 leads. It looks like a smaller version of the TO220 Package.
Please help I've gone back to the manufacture and they have no idea. They purchase these boards assembled.

Thank You in advance.

a picture may help.

Sounds like a SMD Transistor or Regulator,A picture would help,the U58 could be PCB board number?

Looked on web,looks like it is U584 3.3v SMD regulator,06 possibly year?
I have Datasheet,working out how to upload to here??£$%$£$...