Offhand, the only thing I can think of is to just draw one. I've done one in solid that looks like the one you see with shademode on (conical arrow heads). I made it into a block whose insertion point is at the junction of its x,y, & z axis, naturally, so that when inserted at 0,0,0, it looks like the real UCS icon has gone solid - then just scale it so it looks correct in whatever particular view it's in.