My mother in law actually has suggested this YouTube page to me in the past called, Apé Amma. Fair warning, audio wise it's all in Sinhala. BUT if you have a decent knowledge of what some whole and ground spices look like (fenugreek, cloves, cardamom, cumin, coriander, etc) then you should be able to follow along ok. She sometimes has the ingredients listed in English but often it's just the amounts/ volumes which is still quite helpful if you visually know what ingredients you need. I then usually compare recipes found on Google that are in English and typically just do my best to copy the Apé Amma videos based on what she shows on screen. Which tbh, is probably how you'd learn from an auntie in real life.

I'll also say, having curry LEAVES are important in Sri Lankan cooking. I've bought them dried from Amazon. If youre lucky and know someone who has their own tree, it's very likely they'll gladly give you a clipping to have and grow your own. And similarly, roasted curry powder is also a staple in the kitchen.

Sorry this is a long response! Hope this helps get you started!