Carbon steel is the main stay of the straight razor industry. There are a few manufacturer that use stainless as well.

The recently manufactured Thiers Issards for some reason are regarded as more challenging to hone than say vintage razors but personally having owned 2 TI's I haven't seen a difference in how easy or difficult they are to hone i comparison to other recently manufactured straights.

If I were you I would sneak into his shave den and take note of the shapes of his blades. My guess is there will be a trend towards a certain blade width, which we refer to in incriments of 1/8" of inch. Also point style. This should give you a good direction to start in.