I have a aftermarket exhaust from Competition Werkes, e.g. the following item:
BMW R nineT Slip-on Exhaust | 2014-2020 (new ~$550)
And it includes as well the DB Killer insert:
Exhaust Insert db Killer | Large (new ~$40)
Should fit all 2014-2020 Pure, Racer and Urban GS models (according to their website).

The exhaust came with the R Nine T Pure when I bought it. Bike has ~3k miles, therefore I assume that's the max mileage on this exhaust. It's in great condition - check the photos.
Neither the wifey nor the neighbors liked it. :). Your wife or neighbor situation might be different....

Together $250 + shipping.

Cheers, Robert.