I read your post again and realized I didn't really answer your question.
Here is the bayonet lug discussion:
Here are some websites:
Beware of this place, I've heard mixed reviews about this place (I haven't had any problems yet).
<A HREF="http://www.lagger-pro.com" TARGET=_blank>www.lagger-pro.com
As for the metal safety and triggerguard, I've heard that Brownells carrys the parts.