There are many resources on web that you can use to improve your skill.
For starters, you can always ask your questions here; make sure you tag "piano" on your question.
This Youtube channel run by Robert Estrin is also very helpful.
Here is a list of videos on sample sight readings (grade 1-6) and some tips.
Playing an outdoor (rusty) piano in Montreal; near Saint Joseph's Oratory of Mount Royal

Almost every music sheet that you are looking for can be found on musescore.org. Subscription is not free; contact me and I will get the sheet for you.