I bought a Baby Cakes on a whim at a big-box store garden center a few months ago. It had been shipped in a plastic bag, as dormant roots (with a few green leaves) in a neutral medium like sawdust or coconut shavings. The label says "
www.BushelAndBerry.com" as the supplier. If you go to their website, it looks like they use Tractor Supply as their retail outlet in California.
After planting, it does appear to be growing in a tidy cluster, as advertised - not the usual rambling vine style of blackberry.