If weight is your main/only concern the Enve carbon rims with DT aerolites on Tune Princess and Dezibel hubs, should be able to get under a kilo.
Only if you go for the tub rims, which are 260g, at which point you may as well go for Innolite, who do a 230g tub rim, and you may as well use Pillar spokes, and Extralite SPD hubs, certainly on the front, as no one has a production Dezibel yet it’s a moot point, but yes, sub 1000g is doable. Someone on WW did 957g (IIRC) with Innolite XCC250 clinchers.
MMX and a2z you mention, how much roughly and where to get?
Hubs: £120 from any LBS with a Windwave account
Rims: £180 (ish) from CRC etc
Spokes: £40 from Actionsports.de
Build: £60 (say, LBS or builder of your choice)
You’ll need nips too, if you’re not fussed by colours your LBS probably has loads of alu ones – all black DT spokes used to include a box, I know we had literally thousands in stock!