Have a look on any of the big supermarkets' websites - search vegetarian or vegan - there are lots of vegan and vegetarian protein options. I'm relatively new to the vegetarian way of eating but I'm finding tofu, textured vegetable protein products, Quorn, seitan, tempeh, lentils and pulses - all in moderation keep me in the keto range, giving me plenty of protein with a level of carbs that I am currently producing keytones. Its just a question of wanting to eat this way enough (for whatever reason) and then searching for protein alternatives and being open to solutions.