I also have a Polti 2001R. The Security Torx bit required is a T20H. The only place I've managed to find one is http://dkc1.digikey.com/uk/digihome.html - part No 10715-ND.
The part itself is £2.60 but with handling & shipping costs this amounts to around £25-00.
However, Maplin sell a set of security bits which include a T20H, and a separate 150mm Bit holder. I puchased these, but found I had to grind the bit extension to fit the holes in the Polti. The wall of the bit extension was a bit thin but it worked.
Hope this helps.
Andrew Ellis, November 2005