As said Tipo mirrors do fit, not perfectly as the base is slightly smaller but would do the job. Only for the desperate though, they're pretty ugly.
Seen a few 155's with aftermarket mirrors on (e.g.
http://www.cloverleaf4.co.uk/images/uploads/15017.jpg) I would've thought most aftermarket mirrors would fit given the right base plate - these might not be available for the 155 directly but there is probably something similar or something that could be modified a little.
There was a dutch chap who made some BTCC/DTM look mirrors, mentioned on 155.org somewhere.