Audaxing as a vegan is easy in 2017!
I don't understand the issue here.
Firstly, do John Hamilton's events, because he is absolutely top notch for providing masses of vegan food. I was fatter when I finished the Mille Cymru than when I started
Secondly - learn what you can get at all outlets that works well as a fall back - for me, peanuts, prawn cocktail crisps, various chocolate and biscuits are available at even the most basic of forecourts. Most back-of-beyond cafes can knock up baked beans on toast/spud/chips - and that's the worst case. Even in the depths of darkest Wales I normally find a good soya latte nowadays, and a cafe owner keen to help out on the eating front. If there is a supermarket of any type, co-op or an M&S then you are really sorted, loads of vegan options!
Some of my DIYs are so remote I don't actually see a shop or cafe anyway, so I carry enough with me. If you can't carry enough food for a 200 km then there is something seriously wrong somewhere. If you can't fit in flapjacks, veggie sausage rolls, banana, salad and hummus wrap and a bag of barbecue cashew nuts in a jersey, you need a bigger jersey!
Don't forget tho - it's a case of do what you can. So going 'oh, it's too hard, I can't avoid butter on my toast so I may as well stuff as much intensively reared meat into me as possible' makes no sense whatsoever. Saying 'oh, I'm struggling to avoid butter here so I'll eat this toast, but I'll do my best to find something at the next control', makes much more sense. No one is perfect, everyone draws the line where they chose to. I personally would just skip a control rather than eat meat or dairy - but then I'm vegan for ethical reasons. An audax is just a bike ride.....I wouldn't compromise my ethics over something so trivial. Others no doubt would disagree.