Making a homebrew smartwatch sounds like a fun side-project. Any chance you would be willing to share your progress so far? I'm a student with an interest in electronics manufacturing so making one would be more of a learning experience.
Also, for a one-off screen have you looked at contacting a manufacturer on something like Alibaba? They are usually more than willing to send a discounted/free one-off sample of a product.
I looked at a pebble teardown, and saw that it didn't seem to involve very complex production strategies. From that I decided to try building a list of components! I know how to do some microcontroller programming so wasn't too worried about that part, but felt like getting an efficient screen was important.
I've had a hard time finding power efficient screens that I can purchase in very small quantites so I've been stuck there. I've been trawling around parts websites but I almost always end up on things like screens for RasPis.
EDIT: Got some luck on Alibaba searching for "sunlight readable". Going to contact some suppliers to see if I can get something
Also, for a one-off screen have you looked at contacting a manufacturer on something like Alibaba? They are usually more than willing to send a discounted/free one-off sample of a product.