Well your best bet is to get age verified here on the website. Meet up with a local rep, and they'll verify you are 18. Then you get access to the classifieds and the retailers here on the site.
However, with the price range you are looking for, you will be hard pressed to find the things that you want.
Internal battery but with rails and collapsible stock will mean you will need to do your own work on it. Buying a lipo battery and a stock tube that holds a lipo battery.
No other way to get one like that really other than getting AV'd here.
I love freedom and consequently America