Greetings TomK, and welcome aboard,
Congratulations on the acquisition of your new goodies! I'm sure, we're all envious. Most of us get our gear one piece at a time.
Which LEE loader do you have in mind? There are additional safety precautions involved when loading black powder with any brand of loading equipment. I suggest you head over to the Handloading and Reloading Forum and check-out the stickey For the New Reloader: Equipment Basics -- READ THIS FIRST
You're correct about black powder being harder to find these days. One reason is the storage requirements, the new regulations are much less restrictive for black powder substitutes than actual black powder. My neighbor just bought his first BP revolver and went through what you're experiencing. After calling a few regional gun shops, his choices came down to Pyrodex-P (substitute) for $25 or Goex (BP) for $30 a pound.
I ran into a fellow at the gun club who was shooting Goex. He sang the virtues of using real BP over Pyrodex. However, when I asked him where he got his BP he became very evasive. I suspect it wasn't through normal channels and may have involved transporting or storing the stuff in quantities exceeding the safety regulations.
As far as powder substitutes are concerned, you're wearing two hats: With your new guns in their cap and ball mode, you're restricted to black powder and black powder substitutes like the previously mentioned Pyrodex. But, when you use your cartridge conversion cylinders, then you are free to load the metallic cases with black or smokeless powder as per the recipes for cowboy loads.
Have fun and be safe.