Hello there, Karthika! Welcome to planDisney and thank you for bringing us your question.
The Disneyland Resort announced efforts a few years back to reduce plastic waste and removing plastic lids was part of that. So, unfortunately, I do not believe there are lids for the standard-sized fountain drinks. Straws are usually available but have been switched over to paper straws instead of plastic ones.
If having a lid is necessary to you or someone in your party, I would recommend stopping by a
Quick Service location and seeing if they have any Souvenir Sippers, Tumblers, or travel mugs. I've seen a few different kinds throughout the parks. I've noticed
Galactic Grill in Tomorrowland has a Star Wars-themed tumbler from time to time. Other Quick Service locations usually have a Disney-themed sipper. These all will have lids and include a fountain beverage at the time of purchase. You could then just pour your drinks throughout the day into your new sipper. This also makes a great and useful trip souvenir! I love the few Souvenir Sippers I've collected and have used them for years.
Another option would be to bring your own reusable cup with a lid with you to use.
Karthika, thanks again for bringing this question to us. We appreciate you stopping by!
Carrie