I was successful in using a VO 50.4 crankset set up with TA chainrings (42 / 26). VO does not make any smaller chainrings than their stock setup when you purchase it, unfortunately (it comes stock with 46/30). Yes, the setup can end up being a bit pricey, but if you want lower ratios, this is one such solution.
I chose that combo as I installed it on a gravel bike that would see some climbing where we live (foothills of Southern California). It worked okay, but gotta say I might have wished for a bit lower gearing (I ran an 11-speed cassette - 11 / 34).
Since I ran an 11-speed chain, the chain fell between the chainrings with the stock VO hardware and TA rings. I was able to solve this problem by swapping out the stock VO small ring spacers with slightly thinner ones made by Wheels Manufacturing. Shifting is spot-on.
Good luck,
Jeff
Claremont, CA