When we say that 1% of people (for instance) are vegan, that is still quite a lot. That is still millions of potential partners.
If you live in a big city and are willing to use online dating for example, or proactively go to places/clubs where there are likely to be more vegans, to look outside your own existing circles of contacts, then there are still plenty of options. Of course, if you live in a small town or village far from other places it's much harder.