Bad idea.We were thinking of something like sewing a retention holster to the underneath of the chair
The only access would be from the front of the chair (unless it is a powered wheelchair), a difficult reach at best.
The only really practical way to carry a weapon is cross draw. One other possibility would be a holster fastened on the inside of the thigh. Either way it could easily concealed by lap blanket yet accessible by moving the blanket to one side.
Strong side carry is extremely difficult for me and in a wheelchair it would be almost impossible because the chair itself would be in the way.
FWIW, I am not stuck using a wheelchair yet, I do have to use mobility scooters to get around since I can't walk more than 50 feet or so.