Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Lace Rock is usually a form of limestone that has been partially eroded due to water. It will continue to dissolve in your tank, raising the mineral level and the pH.
Go to your local rock yard. (Brick, soil, masonry, landscape...)
Bring some zip-lock bags and a Sharpie pen.
Take samples (broken bits, almost dust that falls off all the time) of whatever you like and label the baggies.
Test at home: Acid test, and put the samples in separate jars with water. Test GH, KH, pH, TDS. Run the test out at least a week, a couple of weeks is better.
Google Rock Yard Orange County CA to find a lot of them.