Keith Wyncoll, of Woodfield Avenue, said the supermarket in Gravesend was unable to provide a wheelchair for his severely autistic eight-year-old son David.
Severely autistic eight-year-old David Wyncoll
Mr Wyncoll, who earlier this year won a Pride in Gravesham award for cultural diversity and understanding, said: "I complained about four months ago that the manual wheelchairs were damaged.
"They have about three of them for use but, for the number of frail or disabled people in Gravesend, I don't think that's enough.
"About two weeks ago I went in and all they had available was the electric ones, not the manual ones, which they said were all away for repair.
"David is a runner and will run away if I'm trying to shop, but when he's in a wheelchair he's quite happy because the world is changing around him.
"They had no wheelchairs whatsoever the other day and I had to use a trolley and he threw himself to the ground five times. It was really a traumatic experience."
The Disability Discrimination Act law requires those who provide a public service, as well as private companies, to make "reasonable adjustments" to allow everyone to use their service. David attends Ifield School, in Cedar Avenue, Gravesend.
Mr Wyncoll, who is project manager of Medway Autism Group and Information Centre, added: "The store manager said he understood where I was coming from but didn't offer any solutions.
"This kind of thing is like shutting the door to disabled people or frail people.
"It's like saying 'you can't come here' and surely that doesn't make good business sense. Business should ensure that their stock of wheelchairs is sufficient for the numbers using the store and that they are regularly maintained."
An Asda spokesman said the store wanted all customers to be able to shop in the most convenient way for them.
A spokesman said: "Each of our 568 stores provides electrical and manual wheelchairs for customers who need them.
"Unfortunately our Gravesend store has had to send its manual wheelchairs away for repairs.
"We apologise to Mr Wyncoll for any upset this has caused him and his family when visiting our store and would like to assure him that two new extra chairs have been ordered for the store and will be ready for customers to use shortly."
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