Marc Carter, 42, from Devon, appealed on Twitter for people to search for a specific Tommee Tippee cup for Ben.
The 13-year-old has severe autism and will only drink out of the two-handle cup which is no longer manufactured.
The appeal prompted offers of help from as far away as Australia from people promising to send Ben their old cups.
Tommee Tippee also said it had a dedicated team looking for the cup in its archive of product samples.
Marc launched a Twitter appeal on Monday under the name @GrumpyCarer in which he said his son had used the specific Tommee Tippee cup since the age of two and would not drink from anything else.
“People say he will drink when he’s thirsty but two emergency trips to A&E with severe dehydration say otherwise.”
Marc told the BBC his son has had his current blue cup for three years, but it is now falling apart and may only last a few more weeks.
He said: “The cup keeps him alive. If we lost the cup and couldn’t find another Ben would die. He would be put on fluids in hospital but he would yank out the tubes.
“This tiny blue cup dictates our life.”
Katie Roden tweeted a photo of the cup she owns, adding: “I have one – here it is! DM me your address and I will send it tomorrow.”
Roslyn Barnett wrote: “I have that exact one my daughter had from being a baby!! Still have it and i can send it to you x”.
Others responded with the suggestion that the cup could be made using a 3D printer if he was able to provide one to be copied.
Marc, who lives near Great Torrington, north Devon, said he had been overwhelmed with the response which saw one of his appeals retweeted 12,000 times.
He said one 16-year-old had used the particular cup as a child and had never wanted to throw it away – but offered to donate it to Ben after seeing the appeal.
The dad-of-three, whose two other children also have special needs, told the BBC: “I cried. It’s been incredible. I didn’t expect it.
“I’ve had people tweeting to say good luck and people looking in their cupboards for the cups. They don’t know me – it’s been amazing and moving.
“I feel humble. It’s a lovely thing. I’m asking for a little blue cup and that is what is touching people.
“I’ve said I’d pay for the postage but people don’t want it.
“Ben might need this cup for the rest of his life so it will be great to have stock. It would be life-changing.”
Full-time carer Marc said he now had around seven replacements being sent to him and hoped to stock up on even more.
Tommee Tippee said it was touched by Ben’s story and staff were doing everything they could to find a cup for Ben.
Sarah Scott, global head of consumer experience, added: “The cup he previously had was a Tommee Tippee cup that we made for Boots in the late 1990s and our team is currently looking through all our archive product samples to see if we have one that’s just right for Ben.”