I won't quite dare to go as far as saying parts will never become a problem ('twould be tempting fate) but....
because the Omega was sold in
such numbers, so as each dies, that's another car's worth of spares to be had, potentially. Also, because so much is shared by run-of-the-mill stuff, Vectras, Astras, and the like, many things are still to be had at motorfactors. Then you realise that the Carlton / Senny before shares much of the underpinnings, too. Thankfully, the Vectra C/Signum kept a development of the V6, so oil coolers etc will be available direct from Vx for a while.
Keep your eye on ebay for the right stuff, we're currently at a point where lots of genuine GM stuff is being cleared out of various Parts depts, now the Omega has reached the 10-year cutoff that Manufacturers are no longer obliged to keep parts for.
I'd advocate to anyone
buy it when it comes up for sale, not because you need it. Otherwise you may find yourself off the road/paying a hefty premium through nesessity. If you get eg: a brand new GM coil pack for £40 (like I did) the worst case is you never need it, you sell the car, and touch wood, someone will have it off you for that kind of money/more, further down the line.