I’m aware not everyone is into making their own supplies. I offer a lot of DIY alternatives for commonly used items but here is one which is purchased rather than made.
I found this at Walmart yesterday while I was looking for drywall tape with round holes in it to make into Punchenella. It is a small plastic tub filled with light and fluffy spackling which you can easily use as modeling paste in your art journals. The cost was less than four bucks for the 8 oz. container.
Here are a few of the pages I used the spackle on in my art journal. These are not finished pages, obviously, but you can see the spackle takes paint beautifully. In this case I used metallic craft paints but any type will work.
Just another low cost alternative to the more expensive modeling pastes marketed to crafters.