Hi,
I know this is an old post but I have found a free padstone calculator, which can be downloaded from;
http://steelbeamcalculator.co.uk/freepadstonecalculator.aspx
Hope this helps others with the same problem.
Saw these on the web;
www.quick-calcs.net from £50 per beam
www.beam-designs.co.uk £60 per beam
www.rivergate.co.uk £40 + vat to £150 + vat
Not sure what there like or their insurance status though.