Try tworog from a Polish shop. You probably want to avoid the lowest fat kind - every package will say, just look for the % figure that will be somewhere reasonably prominent without having to understand the language, or ask the staff. You may want to sieve it before use (depending on the texture).
Wildes cheese make and sell locally. I think they sell at some local delis and farmers markets but I think you can also call in at their dairy near white hart lane for it. Call before to check they’ve got what you need. I know they definitely make curd cheese because I’ve made and eaten it there. I went on a cheese making day course with them and they are excellent and very friendly and knowledgeable chaps.
Thanks for the tips (and thank HoL for being here so that this type of niche question can be aired).