HollisTG
Tell me about it.
I have been begging for help on this site to locate a lime supplier. I did not get many answers:(
Forget about Home Depot. They have nothing you are looking for.
Regular plaster is not lime plaster. It could not possibly be used for frescoes since it sets in a few minutes in the bucket, and that is what plaster de Paris does.
You have to find slaked lime unless you want to slake it yourself.
Slaked lime comes in powder or in putty.
In both cases you have to make sure it has a high content of calcium and it is not hydraulic.
Powder lime is fine specially for limewashes. If you want to produce a high quality stucco or fresco you may want to go with putty lime which is usually more expensive than powdered lime.
Putty lime looks like whipped cottage cheese and is very pleasant to work with.
In both cases you will have to add body to your lime plaster. It will be powedered bricks or rough sand or fine sand or marble powder depending on the thickness you want to achieve.

Buying lime from a chemical supplier and slake it yourself could be a very good choice if you learn first how to handle lime, but the big chemical suppliers are pretty hard to reach and probably do not sell in small amounts.
I am far from having found everything I want at that point.
The only sources I have are three ( spread out) suppliers who sell putty lime ( one of them is imported from Italy) at a fairly high price.
Let me know if you want more info.
Myriam