I can't run the first couple hundred episodes' source because I haven't found those assets anywhere in the files I got when I preordered. Are they available somewhere?

If you follow the sendowl link, there is a "Legacy Files" folder and in that there is a "Handmade Hero Legacy Art Files" download (handmade_hero_legacy_art.zip).
In that zip file there is a "early_data" folder containing the test folders (bmp and wav files).

OMG I feel stupid!! Thanks!