The valves came from an ebay supplier - Performance Closeout. They had listed the 6 cylinder kit for the M5X and I emailed them to see if the could supply just 16 rather than 24. Price was just over $300USD. I went for the single groove valves with collets (part nos BMIVN-1031S and BMEVN-1031S) which are better for high revs.
The TBs are 50mm (huge!) ... 46mm probably would have been better. They line up but will need port matching. Everything downstream of the TBs, ie. ports, valves cams, pistons, headers, exhaust, etca. will need to will need to be appropriately worked on to use all that air from the large TBs. I have someone lined up for the head work.