Brandsport appears to have the full 8 piece flare set in stock, including the front left mudflap, if you feel like spending $600+. Selling off the rest of the flare group on Fleabay to recoup the expense doesn't appear to be a viable option at this time, but YMMV.
The only other stock locations I've found are offshore, and I'm a bit reluctant to give my CC to a Russian Auto Parts dealer (no offense intended).
None of the aftermarket flare sets I've seen for 3g runners have mud flaps, so that gets me nowhere that I want to go as I don't do any wheelin and have major snow to deal with.
Toyota for their part appear not to actually declare a part "discontinued" until all stock is exhausted and no further production is planned, hence the right side being available and the left discontinued. I had to replace the right rear flare this summer due to a collision with a bear (he hit me) and the shop said it was a bear to get the parts (pun intended) and they would soon be discontinued. I suspect the whole flare and flap set will be extinct soon.
I used to work as an engineer in Toyota's supply chain and can tell with absolute candor that starting up production of an old part is a REALLY big deal, and I can understand their reluctance to do so.
I'm working on the 3d scan for the right side and will see if I can get a mirror image printed in ABS. The problem is that the organic shape and black color require that I index the crap out of the thing with white target marks to get a viable scan (the photogrammetry modeling itself is free).
Oh well, I love a 3d modeling challenge. . . if I get it together this winter and have any success I'll post the results and see if I can get a volume discount. I plan on having this vehicle for a looooong time yet.