Yeah, that strap is useless.
Most of us get all our parts from airsoftparts.ca, but a bit of Googling will find you either a US supplier or you can get it from a place like ehobbyasia.com or uncompany.com
I hacked away at the same gun and ended up with a real sweet machine, so all is not lost.
Biggest concern is the handle. This holds the motor, which needs to be held perfectly straight and rigid. You may need to remove it and put in some thin washers and then reinsert the screws in order to hold the handle on straight. Also keep in mind that the motor height may need to be readjusted (using the screw on the centre of the bottom plate of the handgrip.
Sometimes the best way to learn how something works is to break it and then try to fix it. Unfortunately with this gun you will need to exercise those mechanical inclinations of yours- this one can be a bitch to take apart and reassemble.
Get a top rail too and mount a cheap RDS. Here's how mine turned out:
Fires 350 FPS at a wicked ROF with a tuned-up mechbox, tightbore barrel and lipo battery. Do some reading and research on all AEG airsoft guns- these "toys" are as customizable as the neighbour kid's rice-burner.
For more specific parts, it would be a huge help to post up some pictures including some close-ups.