Once you unlock Adventurer mode that doesn't really matter; all vendors are always available I believe.

That said; the fastest way is to make a level 1 game (with the crusader) at the highest difficult level you can handle with your level 23, then invite your level 23 character(s), and just play normally till he catches up. It shouldn't take long. There's a thread here that discusses this; though generally from the perspective of being much higher level.