I bet that 440source doesn't sell them sans springs because it requires a separate SKU/stocking number. The difference of $30 doesn't make economic sense due to potential lost sales from the complete units.
Easier to stock one unit for the marginal difference.
Heck, if I bought them and didn't want the springs/retainers, I'd give them to someone doing a milder build. If $30 is a budget buster?