You’re trying to avoid paying for the rings and the bearings?
Generally, any part that has its own article number can be ordered separately from an official dealer.
However, considering the usual pricing of spares vs retail, it might not save you much, if anything.
As an example: While replacing rings is entirely possible in theory, the cost of a set of separate rings can be higher than picking up a complete crankset on sale.
You might have better luck looking for a used crankset to transfer your rings to.