Kentucky,
This isn't aimed directly at you, but at the many people who ask similar questions without really looking.
I don't understand you not being able to find it ???
Using - "1500 grit silicon carbide "
I did an ebay search and found lots for about $7/lb.
Then I did a google search for "1500 grit silicon carbide powder", and found thousands of internet sources.
If a search does not get you the response you want, use a less defined search.
A search for "1500 grit silicon carbide powder to do a Nick wheeler style hand finish on a 7" bowie knife".....won't get many hits. Even " 1500 grit silicone carbide powder" may be too specific.
Instead of "1500 grit silicon carbide powder", use "1500 grit silicon carbide" That will get you:
1500 grit silicon carbide polish
1500 grit silicon carbide powder
silicon carbide powder
silicon carbide abrasives
and many more.
A search on the basic product will often get you the type of places that use that product, and can lead you to the sources for those industries.
For silicon carbide powder you can discover it is used in lapidary, machining, water jet cutting, abrasive blasting, lens grinding, etc. A check under those topics will find sources. Using wikipedia will often give you lots of ideas and links where you can search.