I read somewhere that you can use store bought ammonia and dry ice to make anhyrdous ammonia. Does anyone know the method?

I don't know about using CO2 but it can be made from ammonium hydroxide (household ammonia) alright. All it is is basifying the household ammonia with sodium hydroxide or a similar base I think.

It tells you how to do it in the Kings Chemistry Survival Guide
http://www.wetdreams.ws/forum/mainuploadsfolder/tina_craig/200622452137_anny.pdf

Looks complicated. Obviously the precursors are easily obtainable but synthesizing NH3 is dangerous as fuck without the proper equipment and knowledge. eres a thread talking about it
http://www.wetdreams.ws/forum/topic.asp?TOPIC_ID=1945&whichpage=1
I came across a few threads on drugs-forums about NH3 production but I couldn't be bothered looking for them right now.

Salt, precipitate, swap base, dry gas, refrigerate as needed.

...it's pretty much on the "basics" end of chemistry...

literally.