Hi Andrew,
Does the attached look OK? I imported your jpeg into Autocad and did a quick trace over. The curves are arcs and not splines so I could make each character into a polyline.
The characters are 10mm high so you could scale them to whatever height you like.
The zip file contains the dxf - I seemingly can't attach a dxf directly.
[Edit: Replaced zip file - a rogue line was removed.]
Phil.