There hasn't been an official MSE-6 Repair Droid released in the 6" Black Series range, but that doesn't mean there isn't one out there in perfect 1/12 scale.
At the back end of the Kenner POTF Freeze Frame releases in 1999 a Death Star Droid was put out in 3.75" scale, packed with an MSE Droid. At the time the MSE droid was grossly overscaled to the 3.75" range. He would be repacked later in with R4-M9 in the Power of the Jedi range, and again in a Death Star Accessory Pack.
The MSE droid, according to Star Wars Wiki, stands 25cm in height. At 1/12 scale this would have him standing 2cm high, the exact height that this Kenner released MSE droid sits - what a lovely coincidence.
Sculpt wise the MSE is a tad soft and is a single hollow piece with moulded wheels. The sides contain the computer panels that we do see light up in the onscreen counterpart. There are two aerial sections on the top, but these are simple flat panels on the figure. There is also a mould line that runs the length of the figure where the two halves have been factory assembled.
Ok, so he is not perfect and he is showing his age. But if you want to accessorize your Imperial Display, then finding these is not overly difficult on eBay. Most will need a good clean, they certainly attract dust, but once sorted will sit happily at the feet of your Stormtroopers or even Krennic himself in a Rogue One Display.