I went to http://sketchup.google.com/3dwarehouse/ and searched and found quite a few asronauts/spacemen.

After you find some .skp models, download and install Google Sketchup; it will run for free for 8 hours- plenty of time to export the models as .obj files which work perfectly in Poser, although they will not be posable.

I wouldn't buy Sketchup- it doesn't conform to any 3d package conventions and costs a whopping $450. You get a heck of a lot more bang for your 3D dollars with most other packages (free or commercial!) but there are some super models available.