Actually, most weapons I see on here are either made from scratch (like tactonyx or redshirt), or machined out with vector/cad files designed (Justinian, me to a small extent). You will find that the process of pepping weapons is very difficult and does not yield very nice results. I tried doing the needler in pep and it was a nightmare..
If you want something for a kid, it might be worth tracking one of these down:
http://i580.photobucket.com/albums/...o Armor/toyHaloAssaultRifle-PlasmaBlaster.jpg
Painted, they are very good kid-sized copies of the halo assault rifle (the company got in trouble for the similarities to the halo AR)
Lastly, I understand there is a drive to make something neat for your kid, but you come off a bit aggressively, saying you refuse to use a windows machine to do it yourself, and then posting over and over asking other people to size and pdf print files for you to leaf through is a bit much.
While people on the 405th try their best to render aid, usually members only have the time and inclination to give advice and help in spoken word. When you want something extensive like any work with 3d models, custom pep files, or manual services rendered, you will get much faster results doing it yourself. It's not that they don't want to help people, but most of us have school, jobs, blah blah blah, and what time is left goes primarily to our own endeavors first.
As was mentioned to you earlier, you can take a thumb drive to a library, install pepakura designer on that, and then use it to resize and pdf print models to your heart's content. This will be your best option if you won't be getting personal access to a windows machine.