I came across the site of a fellow in England that stamps reproductions of historic coins from Celtic to Tudor time periods. Although their finished coins are not cheap, they seem to be good quality - and he sells dies as well. While there may be plenty of folks doing this, I haven't been involved too much in this pursuit, so I thought I would throw it out there just in case. My thought was that he might serve as a good resource as a quality die maker, though he isn't in the states which I realize is a downside since shipping this stuff isn't going to be cheap. A set of his dies (pile, trussel, and striking collar) for a portrait style coin is 400 pounds, so... not cheap. However, he does say that he sometimes has used dies which might be worth investigating.

Grunal Monetta's Mint
http://www.grunal.com

Another cool thing he offers is a Money Bag of up to 10 coins from a given time period for 7 pounds. Obviously, we'd be interested in the Roman-Celtic one.