I need a downloadable graphic of a large arrow, at least 450 pixels
wide, and preferably arced.  A tapering cometlike tail would be an
excellent plus but is probably too much to ask.  I prefer a solid
color so I can do with it what I choose, but I won't be picky about
that; the shape is the main thing.  I can find tons of arrow graphics
out there, but not big ones.  And a small one enlarged won't do unless
the outline remains smooth.

Thank you for inviting me to post an answer, Archae0pteryx.
  
I hope you got some usage from the image I created. If I can assist
you in any way further, please let me know.
    
All the best,
   
Jackburton

Thanks, this was fine.  I made the modifications myself, and they
weren't beautiful, but they sufficed.  Going by what was in my
question, you supplied exactly what I asked for.

Thank you,
Archae0pteryx

Will this do?...
  
http://img2.exs.cx/img2/4518/arrow1.jpg

The form and size are excellent, jackburton.  The silhouette is not
smooth, though; you can see the jagged pixel outline.  I think what
this means is that I need a vector-based instead of bitmap-based
image.  But I was not careful to specify the preference for a smooth
outline in my question, so I can't fault your response.  It's only
fair for me to accept with thanks your answer as given.

Just in case you made this yourself instead of finding it, though,
could I ask for a couple of changes?

Thank you,
Archae0pteryx

I would be happy to amend the image for you, but since my graphic
design skills are limited, I would prefer to leave the question open
to other researchers, in case someone who is more proficient can serve
you better.

Never mind, Jack, I am already working with it as is, so this one's
yours.  Please post your answer.

Thanks,
Archae0pteryx

for a few $ you can choose from 100,000+ images at www.istockphoto.com
they have hundreds of arrows !

I can also recommend www.dreamstime.com who are cheaper for larger
images... Just $1 an image. you cant beat that.