Farmer,
Your best bet for dies is to call a manufacturer and ask them if they have them on hand. I do know that Redding and RCBS both list them.
I went through this when I built my 6.5-06AI and The prices were High, around $150 either manufacturer.
I ended up going with RCBS, not because they were better, but because they actually had a set on hand. Redding more often than not has to make them and there is a significant wait time.
As far as brass goes. Not sure you can just neck down the .243AI brass (I have one of them too). shoulder placement might be an issue as well espcecially at the shoulder neck juncture. Might not be able to chamber properly, and head space might be an issue. you would just have to give it a try i guess.
Dan