Round Rail Mount Kit
The round rail kits have been discontinued, but you can find basically the same thing at www.folbe.com here. With the folbe kit only the top two bolts of the V-Lock will line up correctly, that should be enough to hold most applications.
If your experience is that two bolts does not provide enough support, there is a V-Lock-to-Folbe adapter to match the bolt patterns for the V-Lock Base to the Folbe Rail Kit.
Does not include a V-Lock Base
Yes, there is a base in the picture but for illustrative purposes only.