There are 3 or 4 options for this and which you choose depends on your budget and how sturdy you want it to be. CDI precision mentioned above is a solid choice. Pacific Tool and Gauge has 1 that comes with a 3006 DMB and bottom metal for $100. It does need a little work on the mag to work with the bottom metal, but it's held up fine for me; I'm running it in a 3006 myself. Wyatt's DBM are another though they are notoriously long due to single stack design. The last one I found was HS Precision pro steel. All of these companies sell BDL drop in DBM systems with a 3006 in mind.
There are of course a lot more options, but not any more options I'm aware of that are drop in to BDL inlet. CDI gets a pass since they'll inlet for free.
